Interested in high-performance tube-based AM tuner designs
 

[New Yahoo Group started: "AM Tube Tuners". See end of this message
for more info.]


In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

(Obviously, a stereo FM tube tuner will be of even more interest to
the tube-o-philes, but there is also a market for an AM tube tuner.
Some may prefer an integrated AM/FM tube tuner, and that's fine, too,
but my focus here is on MW/BCB -- it certainly has special needs
requiring dedicated design even if it is incorporated into an AM/FM
tuner.)

What sort of specs should this AM tuner have? Well, that is certainly
a very open-ended question, with no right answer. However, I believe
the following preliminary list of qualitative specs and requirements
essentially outlines the likely preferred parameter space for the
typical expectations of those who will build and use this AM tube
tuner. Undoubtedly this list is very preliminary, and will be improved
as the experts weigh in (I am NOT an expert on AM tuners), hopefully
even adding real numbers to the resultant specs and requirements.

1) Excellent audio quality at the line-out, effectively reproducing,
with acceptably low distortion, the full fidelity of the broadcast.

(The tuner itself, unlike the radios of yesteryear, will not have
a final audio amplifier stage -- it is assumed the line out will
connect to an audiophile-grade sound system. Low noise is important
since the audiophile system will certainly resolve any noise
present.)

2) Sensitivity, selectivity, etc., will also be quite good, so with an
appropriate antenna, the tuner will be usable for casual MW DXing.

(Obviously it will not, and should not, compete with high-end gear
used for serious MW DXing, such as the Drake R8B and a modded ICOM
R75, to name a couple. But on the other hand, the design should be
"fun" to listen to when the AM band happens to be active at night
-- it should at least be comparable to my venerable RS DX-399 with
RS 15-1853 AM Loop.)

3) The kit/design should be relatively easy (for those experienced
with building audiophile tube amps/pre-amps), and not require a lot
of effort, expertise and new knowledge to construct, align and
adjust, nor require constant adjusting to keep it tuned once built.
The number of tubes in the AM tuner probably should be kept low
(4-6 tubes are preferable by my lay reckoning -- it does help that
there is no final stage audio amplifier.)

(I envision that with the right design, ready-made PCB boards can
be built, like what diytube makes for its amplifiers, for the AM
tube tuner -- to make the design reasonably "fool proof". Obviously
issues not seen in audio amplifiers, such as RF/IF interference,
have to be specially dealt with -- multiple, shielded boards?
Clearly a high-quality AM tuner is a step above audio amplifiers in
complexity and potential problems, but those already skilled in
building tube amps should be able to move to the next level to
assemble the AM tuner and get it working.)

4) The design should specify parts which can be bought new today at
reasonable prices. That means: NO SCROUNGING NEEDED for parts (such
as from old radios on eBay.) Many who will build the AM tuner will
not be old radio collectors, and thus prefer all new, modern parts.
The tubes should be commonly available.

(For example, it appears that multigang tuning capacitors are still
manufactured today by several manufacturers. The components which
require special construction are RF and IF coils. Maybe with a good
design, someone may be able to have a bunch of them made to specs
for use in the kits?)


Strategy and Issues as I see them now:

As noted above, I am clearly not an expert on AM tuners, although I've
been studying whatever resources are available on the Internet,
learning about the designs of yesteryear and those who are trying to
push the envelope with today's better components. Thus, I hope that
the experts here, who have actually built radio tuners and know their
stuff, will take an interest in this. Obviously the first step is to
better state (and later quantify) the requirements and specifications
as attempted above.

However, I can certainly suggest some things which appear important to
discuss (and this list is not prioritized, nor exhaustive), such as:

1) Should we simply find a suitable radio/tuner from yesteryear and
"modernize" it? From the late 30's through the 50's, there are
certainly many worthy candidates to choose from.

Of course, let's begin suggesting candidates!

2) Basic type of receiver. For example, should we consider TRF, or
stick with superheterodyne? TRF, especially using modern components
and modern design, is actually intriguing after reading many of
the messages by John Byrns and others. It potentially can have very
high fidelity audio (from an audiophile sense it is a "purer"
architecture), and does not generate IF interference which again
may turn off audiophiles worried about that. The downsides are
well-known (mainly with selectivity, requiring several carefully
tuned stages to have acceptable selectivity), but there are
workarounds. Superheterodyne is the tried and true receiver type,
with a seemingly endless number of good commercial designs to
choose from. And since simplicity of circuit design is preferred,
would a "supercharged and modernized" AA5 circuit meet the specs?

3) Variable bandwidth control. It appears that a user-adjustable
bandwidth control is called for, especially for switching between
local high-power stations, and weaker distant stations.

4) Antenna input, and antenna gain control? I envision the tuner to
be flexible in the kind of antenna types it will be able to handle.
The types of antennas I've seen used for MW include a ferrite rod,
a simple wire (both can be augmented with, for example, a Radio
Shack AM Loop antenna 15-1853), and more fancy antennas such as
the active loop antennas by Wellbrook (see
http://www.wellbrook.uk.com/products.html#ALA1530 ). I would
assume that an antenna gain control will be needed, but then maybe
not.

5) One problem with building a tuner to cover the MW band is that it
must cover over a 3x span, from about 500khz to 1800khz. This seems
to negatively impact on some receiver designs. Interestingly, has
anyone considered breaking up the BCB band into multiple bands, for
example three bands (500-800, 800-1200, and 1200-1800khz)? Would
doing this confer benefits for some receiver types?

6) Another interesting possibility is that the tuner will almost
exclusively be used to receive commercial broadcasting. In most
of the world, and especially in North America and Europe,
broadcasting is done in very specific frequencies (every 10khz
in the U.S., every 9khz in Europe). So one can envision that
instead of using a multigang tuning capacitor or inductor, to
prewire each channel, specifically tuned for a specific broadcast
frequency -- then have a switch to switch between the channels.
This is especially intriguing for multi-stage TRF designs. Of
course, for the U.S. this would mean over 120 such channels, and I
assume more for Europe. Could get to be unwieldy and calibration
may be an issue -- but then the cost and space of multigang
variable capacitors is significant.

7) A hybrid digital/tube system may be acceptable to the audiophiles.
Any advantages here?

(But there is something to be said for using only components which
are similar to those used in classic radios -- an aesthetic issue
important to some. After all, many well-designed solid state AM
tuners are excellent performers, so restricting ourselves to tubes
is arguably an "aesthetic decision".)


If anyone is interested, I've created a YahooGroup to discuss this
further in a dedicated forum. If you already have a YahooID, you can
subscribe to it via:

http://groups.yahoo.com/group/am-tube-tuners/

If you don't have a YahooID, send a blank email to:



Hope to see you there.


I look forward to your feedback, thoughts, and, yes, candid
criticisms!

Jon Noring

Jon,

Wow! Long wish list. You can boil your list down to two requirements:
1. Very low distortion introduced by your ideal tuner.
2. No audio rolloff up to 5kHz.

There have been a number of threads in this group concerning distortion
introduced by the receiver detector stage. Do a Google groups search to
find them.

AM broadcast stations are required to cut off their high audio frequency
abruptly at 5kHz to prevent interference to adjacent channels spaced +
or - 10kHz. You won't find high fidelity among the AM stations no matter
how good your tuner. The best you can hope for is a tuner that doesn't
add it's own frequency response limitations below 5kHz. Do you really
want more than 5KHz response to listen to Rush? (I think a high
frequency limit of, say, 20 Hz would be more appropriate for his show).

Otherwise, I like your Yahoo groups idea. It's a great idea to provide a
forum for discussion of your ideas. It will serve to educate all
participants.

Phil B

"Jon Noring" wrote in message
...
[New Yahoo Group started: "AM Tube Tuners". See end of this message
for more info.]


In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

(Obviously, a stereo FM tube tuner will be of even more interest to
the tube-o-philes, but there is also a market for an AM tube tuner.
Some may prefer an integrated AM/FM tube tuner, and that's fine, too,
but my focus here is on MW/BCB -- it certainly has special needs
requiring dedicated design even if it is incorporated into an AM/FM
tuner.)

What sort of specs should this AM tuner have? Well, that is certainly
a very open-ended question, with no right answer. However, I believe
the following preliminary list of qualitative specs and requirements
essentially outlines the likely preferred parameter space for the
typical expectations of those who will build and use this AM tube
tuner. Undoubtedly this list is very preliminary, and will be improved
as the experts weigh in (I am NOT an expert on AM tuners), hopefully
even adding real numbers to the resultant specs and requirements.

1) Excellent audio quality at the line-out, effectively reproducing,
with acceptably low distortion, the full fidelity of the broadcast.

(The tuner itself, unlike the radios of yesteryear, will not have
a final audio amplifier stage -- it is assumed the line out will
connect to an audiophile-grade sound system. Low noise is important
since the audiophile system will certainly resolve any noise
present.)

2) Sensitivity, selectivity, etc., will also be quite good, so with an
appropriate antenna, the tuner will be usable for casual MW DXing.

(Obviously it will not, and should not, compete with high-end gear
used for serious MW DXing, such as the Drake R8B and a modded ICOM
R75, to name a couple. But on the other hand, the design should be
"fun" to listen to when the AM band happens to be active at night
-- it should at least be comparable to my venerable RS DX-399 with
RS 15-1853 AM Loop.)

3) The kit/design should be relatively easy (for those experienced
with building audiophile tube amps/pre-amps), and not require a lot
of effort, expertise and new knowledge to construct, align and
adjust, nor require constant adjusting to keep it tuned once built.
The number of tubes in the AM tuner probably should be kept low
(4-6 tubes are preferable by my lay reckoning -- it does help that
there is no final stage audio amplifier.)

(I envision that with the right design, ready-made PCB boards can
be built, like what diytube makes for its amplifiers, for the AM
tube tuner -- to make the design reasonably "fool proof". Obviously
issues not seen in audio amplifiers, such as RF/IF interference,
have to be specially dealt with -- multiple, shielded boards?
Clearly a high-quality AM tuner is a step above audio amplifiers in
complexity and potential problems, but those already skilled in
building tube amps should be able to move to the next level to
assemble the AM tuner and get it working.)

4) The design should specify parts which can be bought new today at
reasonable prices. That means: NO SCROUNGING NEEDED for parts (such
as from old radios on eBay.) Many who will build the AM tuner will
not be old radio collectors, and thus prefer all new, modern parts.
The tubes should be commonly available.

(For example, it appears that multigang tuning capacitors are still
manufactured today by several manufacturers. The components which
require special construction are RF and IF coils. Maybe with a good
design, someone may be able to have a bunch of them made to specs
for use in the kits?)


Strategy and Issues as I see them now:

As noted above, I am clearly not an expert on AM tuners, although I've
been studying whatever resources are available on the Internet,
learning about the designs of yesteryear and those who are trying to
push the envelope with today's better components. Thus, I hope that
the experts here, who have actually built radio tuners and know their
stuff, will take an interest in this. Obviously the first step is to
better state (and later quantify) the requirements and specifications
as attempted above.

However, I can certainly suggest some things which appear important to
discuss (and this list is not prioritized, nor exhaustive), such as:

1) Should we simply find a suitable radio/tuner from yesteryear and
"modernize" it? From the late 30's through the 50's, there are
certainly many worthy candidates to choose from.

Of course, let's begin suggesting candidates!

2) Basic type of receiver. For example, should we consider TRF, or
stick with superheterodyne? TRF, especially using modern components
and modern design, is actually intriguing after reading many of
the messages by John Byrns and others. It potentially can have very
high fidelity audio (from an audiophile sense it is a "purer"
architecture), and does not generate IF interference which again
may turn off audiophiles worried about that. The downsides are
well-known (mainly with selectivity, requiring several carefully
tuned stages to have acceptable selectivity), but there are
workarounds. Superheterodyne is the tried and true receiver type,
with a seemingly endless number of good commercial designs to
choose from. And since simplicity of circuit design is preferred,
would a "supercharged and modernized" AA5 circuit meet the specs?

3) Variable bandwidth control. It appears that a user-adjustable
bandwidth control is called for, especially for switching between
local high-power stations, and weaker distant stations.

4) Antenna input, and antenna gain control? I envision the tuner to
be flexible in the kind of antenna types it will be able to handle.
The types of antennas I've seen used for MW include a ferrite rod,
a simple wire (both can be augmented with, for example, a Radio
Shack AM Loop antenna 15-1853), and more fancy antennas such as
the active loop antennas by Wellbrook (see
http://www.wellbrook.uk.com/products.html#ALA1530 ). I would
assume that an antenna gain control will be needed, but then maybe
not.

5) One problem with building a tuner to cover the MW band is that it
must cover over a 3x span, from about 500khz to 1800khz. This seems
to negatively impact on some receiver designs. Interestingly, has
anyone considered breaking up the BCB band into multiple bands, for
example three bands (500-800, 800-1200, and 1200-1800khz)? Would
doing this confer benefits for some receiver types?

6) Another interesting possibility is that the tuner will almost
exclusively be used to receive commercial broadcasting. In most
of the world, and especially in North America and Europe,
broadcasting is done in very specific frequencies (every 10khz
in the U.S., every 9khz in Europe). So one can envision that
instead of using a multigang tuning capacitor or inductor, to
prewire each channel, specifically tuned for a specific broadcast
frequency -- then have a switch to switch between the channels.
This is especially intriguing for multi-stage TRF designs. Of
course, for the U.S. this would mean over 120 such channels, and I
assume more for Europe. Could get to be unwieldy and calibration
may be an issue -- but then the cost and space of multigang
variable capacitors is significant.

7) A hybrid digital/tube system may be acceptable to the audiophiles.
Any advantages here?

(But there is something to be said for using only components which
are similar to those used in classic radios -- an aesthetic issue
important to some. After all, many well-designed solid state AM
tuners are excellent performers, so restricting ourselves to tubes
is arguably an "aesthetic decision".)


If anyone is interested, I've created a YahooGroup to discuss this
further in a dedicated forum. If you already have a YahooID, you can
subscribe to it via:

http://groups.yahoo.com/group/am-tube-tuners/

If you don't have a YahooID, send a blank email to:



Hope to see you there.


I look forward to your feedback, thoughts, and, yes, candid
criticisms!

Jon Noring

Jon Noring wrote:

[New Yahoo Group started: "AM Tube Tuners". See end of this message
for more info.]

In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

(Obviously, a stereo FM tube tuner will be of even more interest to
the tube-o-philes, but there is also a market for an AM tube tuner.
Some may prefer an integrated AM/FM tube tuner, and that's fine, too,
but my focus here is on MW/BCB -- it certainly has special needs
requiring dedicated design even if it is incorporated into an AM/FM
tuner.)

What sort of specs should this AM tuner have? Well, that is certainly
a very open-ended question, with no right answer. However, I believe
the following preliminary list of qualitative specs and requirements
essentially outlines the likely preferred parameter space for the
typical expectations of those who will build and use this AM tube
tuner. Undoubtedly this list is very preliminary, and will be improved
as the experts weigh in (I am NOT an expert on AM tuners), hopefully
even adding real numbers to the resultant specs and requirements.

1) Excellent audio quality at the line-out, effectively reproducing,
with acceptably low distortion, the full fidelity of the broadcast.

(The tuner itself, unlike the radios of yesteryear, will not have
a final audio amplifier stage -- it is assumed the line out will
connect to an audiophile-grade sound system. Low noise is important
since the audiophile system will certainly resolve any noise
present.)

2) Sensitivity, selectivity, etc., will also be quite good, so with an
appropriate antenna, the tuner will be usable for casual MW DXing.

(Obviously it will not, and should not, compete with high-end gear
used for serious MW DXing, such as the Drake R8B and a modded ICOM
R75, to name a couple. But on the other hand, the design should be
"fun" to listen to when the AM band happens to be active at night
-- it should at least be comparable to my venerable RS DX-399 with
RS 15-1853 AM Loop.)

3) The kit/design should be relatively easy (for those experienced
with building audiophile tube amps/pre-amps), and not require a lot
of effort, expertise and new knowledge to construct, align and
adjust, nor require constant adjusting to keep it tuned once built.
The number of tubes in the AM tuner probably should be kept low
(4-6 tubes are preferable by my lay reckoning -- it does help that
there is no final stage audio amplifier.)

(I envision that with the right design, ready-made PCB boards can
be built, like what diytube makes for its amplifiers, for the AM
tube tuner -- to make the design reasonably "fool proof". Obviously
issues not seen in audio amplifiers, such as RF/IF interference,
have to be specially dealt with -- multiple, shielded boards?
Clearly a high-quality AM tuner is a step above audio amplifiers in
complexity and potential problems, but those already skilled in
building tube amps should be able to move to the next level to
assemble the AM tuner and get it working.)

4) The design should specify parts which can be bought new today at
reasonable prices. That means: NO SCROUNGING NEEDED for parts (such
as from old radios on eBay.) Many who will build the AM tuner will
not be old radio collectors, and thus prefer all new, modern parts.
The tubes should be commonly available.

(For example, it appears that multigang tuning capacitors are still
manufactured today by several manufacturers. The components which
require special construction are RF and IF coils. Maybe with a good
design, someone may be able to have a bunch of them made to specs
for use in the kits?)

Strategy and Issues as I see them now:

As noted above, I am clearly not an expert on AM tuners, although I've
been studying whatever resources are available on the Internet,
learning about the designs of yesteryear and those who are trying to
push the envelope with today's better components. Thus, I hope that
the experts here, who have actually built radio tuners and know their
stuff, will take an interest in this. Obviously the first step is to
better state (and later quantify) the requirements and specifications
as attempted above.

However, I can certainly suggest some things which appear important to
discuss (and this list is not prioritized, nor exhaustive), such as:

1) Should we simply find a suitable radio/tuner from yesteryear and
"modernize" it? From the late 30's through the 50's, there are
certainly many worthy candidates to choose from.

Of course, let's begin suggesting candidates!

2) Basic type of receiver. For example, should we consider TRF, or
stick with superheterodyne? TRF, especially using modern components
and modern design, is actually intriguing after reading many of
the messages by John Byrns and others. It potentially can have very
high fidelity audio (from an audiophile sense it is a "purer"
architecture), and does not generate IF interference which again
may turn off audiophiles worried about that. The downsides are
well-known (mainly with selectivity, requiring several carefully
tuned stages to have acceptable selectivity), but there are
workarounds. Superheterodyne is the tried and true receiver type,
with a seemingly endless number of good commercial designs to
choose from. And since simplicity of circuit design is preferred,
would a "supercharged and modernized" AA5 circuit meet the specs?

3) Variable bandwidth control. It appears that a user-adjustable
bandwidth control is called for, especially for switching between
local high-power stations, and weaker distant stations.

4) Antenna input, and antenna gain control? I envision the tuner to
be flexible in the kind of antenna types it will be able to handle.
The types of antennas I've seen used for MW include a ferrite rod,
a simple wire (both can be augmented with, for example, a Radio
Shack AM Loop antenna 15-1853), and more fancy antennas such as
the active loop antennas by Wellbrook (see
http://www.wellbrook.uk.com/products.html#ALA1530 ). I would
assume that an antenna gain control will be needed, but then maybe
not.

5) One problem with building a tuner to cover the MW band is that it
must cover over a 3x span, from about 500khz to 1800khz. This seems
to negatively impact on some receiver designs. Interestingly, has
anyone considered breaking up the BCB band into multiple bands, for
example three bands (500-800, 800-1200, and 1200-1800khz)? Would
doing this confer benefits for some receiver types?

6) Another interesting possibility is that the tuner will almost
exclusively be used to receive commercial broadcasting. In most
of the world, and especially in North America and Europe,
broadcasting is done in very specific frequencies (every 10khz
in the U.S., every 9khz in Europe). So one can envision that
instead of using a multigang tuning capacitor or inductor, to
prewire each channel, specifically tuned for a specific broadcast
frequency -- then have a switch to switch between the channels.
This is especially intriguing for multi-stage TRF designs. Of
course, for the U.S. this would mean over 120 such channels, and I
assume more for Europe. Could get to be unwieldy and calibration
may be an issue -- but then the cost and space of multigang
variable capacitors is significant.

7) A hybrid digital/tube system may be acceptable to the audiophiles.
Any advantages here?

(But there is something to be said for using only components which
are similar to those used in classic radios -- an aesthetic issue
important to some. After all, many well-designed solid state AM
tuners are excellent performers, so restricting ourselves to tubes
is arguably an "aesthetic decision".)

If anyone is interested, I've created a YahooGroup to discuss this
further in a dedicated forum. If you already have a YahooID, you can
subscribe to it via:

http://groups.yahoo.com/group/am-tube-tuners/

If you don't have a YahooID, send a blank email to:



Hope to see you there.

I look forward to your feedback, thoughts, and, yes, candid
criticisms!

Jon Noring

Building tuners for AM, ( including stereo AM )
and FM stereo tuners to suit the Zenith system used internationally
is a fine project for the diyer, except it does take a very deep working
knowledge of
coil winding for RF, 88-108MHz, 550kHz to ,1,700kHz, IF transformers,
both 455 kHz, and 10.7 kHz, and discriminator coils, and 19 kHz and 38 kHz
coils,
plus all the LC filters used for the stereo decoder.
As soon as ppl have to get off their butts and understand and wind coils
for all these F, they give up,
because its too hard, and there is simply so much to know, and it all
takes months to get anywhere.

In 10 years of being interested in such things, I have found almost zero
interest world
wide in ppl wanting to build an AM radio from start to finish, and
I have and only 3 enquiries about the workings of the FM MPX decoder
I have at my webpages in the 4 years I have had a website going.

I do have a schematic of a decoder at
http://www.turneraudio.com.au/htmlwe...mpxdecoder.htm

Anyone is welcome to try to build what I made up from parts in a Trio
receiver, which originally gave the most appalling stereo decoding when I
bought
it second hand for $100.

My design is totally different to anything by Trio.

I don't really want to spoonfeed anyone with helpful information to build
such a thing
unless they are well prepared as I was to do all their own research in
their local university archive libraries
which will maybe have much of the 1960s info about how this stuff actually
works.

I have reams of info in hard copy form which I photocopied.
I have had a second decoder on the drawing boards for 4 years, which
should give lower
mono to stereo thd conversion, and clearer audio.

There are some hi-fi AM tuners which were all solid state, the AudioLab
was one such
which had wide AF bandwidth and low thd.

Stereo AM using tubes would be quite a challenge, but why oh why?
I don't think the programmes I listen to on my home made AM radio
warrant the effort involved to get a stereo signal.

To build a tube based AM tuner for mono is a nice project, and
one can re-cycle the litz wire RF input coils and 455 kHz IFTs.

The info about increasing the pass bandwidth of IFTs is in RDH4, and it
involves a
a switched tertiary winding of a few turns on IFTno1 of an existing set
How this works out
for the diyer depends on the tenacity and discipline which is employed to
measure the IF bandwidth.

The tubed superhet I found was the best type of radio for AM.
Forget TRF, or direct conversion using tubes, ie, the synchrodyne of
homodyne receiver.

The input coils ahead of a converter tube like a 6BE6 or 6AN7
need to have a pass band at all RF frequencies of about 20 kHz each side
of the station F,
so I used two cascaded LC circuits, slightly stagger tuned to get wide BW
at the LF end of
the band where a single LC circuit has too high a Q and causes sideband
cutting, and audio attenuation
of the transmitted modulation.
Anyone not understanding what I just said should hurry off to their
library to find out;
I ain't interested in doing your home work for you.

The IFTs found in most old sets are usually 455 kHz.

To widen the poor natural BW of these tuned LC transformers,
the tertiary can be used on IFT1, as described in RDH4,
or the LC circuit can have its Q reduced by placing a 100k zcross each LC
circuit.
Experimenters will find the right value of R to reduce the Q.
But the downside is that the skirt selectivity will suffer, and stations
only
50 kHz away from the wanted signal will be heard, so add another IF stage
with R damped
LC circuits.

With luck, maybe you will squeeze a bandwidth of 14 kHz after all these
tuned circuits,
and this allows 7 kHz of audio, -3dB point.
The rate of attenuation beyond the 3 dB point is severe, and has a huge
amount of phase shift
This can be reduced a little with an RC step filter which boosts the
treble at 6 dB/octave
after a pole at 7 kHz, and perhaps you can extend the recovered audio out
to 9 kHz.

I tried fitting 9 kHz notch filters to remove the whistles heard on DX
listening, but
it does not remove very much except the carrier interference; the
modulation of a station on a nearby
F still gets through.

Stations here in Oz are 9 kHz apart.

Some are allowed to modulate their carriers with whatever is on the CD.
Others are limited, because the sidebands of stations only 9 kHz apart
will interfere if the modulation audio extends beyond 4.5 kHz for each
station.

The basic problem with distance listening of AM is that there are so many
stations.
I don't bother with DX AM, and since all the stations are networked, there
is no point
listening to rock and roll from MP3 at reduced audio BW from hundreds of
miles away
when the same trash can be heard locally, which bores me to tears anyway.
Noise ruins most DX listening, and the hums and buzzes from switchmode
power supplies
all around the local area.

I only listen to the govt owned ABC stations because their news and public
affairs info is good,
and there is no advertising, and no blue collar based lowest common
denominator redneck
low grade talkback shows spaced between adverts I cannot tolerate.

My set has a dual stagger tuned RF input, an RF amp using a triode
CF feeding a grounded grid triode amp resistively loaded with 22k, from
which the
tuned RF signals are RC fed to the 6AN7 converter grid.
The 6AN7 has cathode bias.
The basic selectivity prior to the converter prevents a powerful station
cross-modulating the wnated lower power station.

Then I have two IFTs with R damped windings, but No1 has variable distance
adjustment
between the two coils to slightly increase coupling to increase the BW.
The IF amp is 6BX6 set up with cathode bias with no AVC applied,
and the amplification is as linear as possible.
The AVC voltage is only applied to the RF amp.
After the last IF LC, I have a CF triode buffer which powers a germanium
diode detector,
with the diode biased on at all times with a small current to avoide diode
distortions at low levels of signal.
This is followed by a second CF buffer and RC step filter to boost the
audio at HF,
and a tone control to adjust treble +/- 6 dB, needed because many
programmes
need such adjustment.
The bass response is good down to 10 Hz.
The thd is very low, leaving the thd and compression and limiting effects
used by the station to
be heard in all their glorious ugliness, when they are used.

My set has a trioded EL34 and 12AX7 paralleled to make a normal feedback
audio amp
with a 1953 12" speaker in reflex box of about 60 litres,
with a 1972 dome tweeter for above 5 kHz.

Better AM reception I have not heard.

The set is able to produce many volts of audio at quite low thd,
but I have it set up to make only about 2vrms max, to keep the thd low,
but also
enough to climb above the set noise.

The antenna is a peice of wire about 3M long.

Directional antennas might be better, but the only hassle I mainly have is
with some
local ******* who has a switchmode PS which puts out a buzz ridden version
of
the stations I like to listen to. This is an increasing problem despite CE
legislation to
compel asian made crap from causing radio interferences.

I have been sitting happy at breakfast when this ******* turns on his
gear, and BZZZZZ.
It ain't my set's PS, because it has a lot of capacitance in the PS, and
it runs on a few secs after turnoff.
So when I turn it off, the hum continues, so the buzz isn't from my PS.

I earthed my set well to a water pipe just below where the radio is, but
still I get it.
Maybe the water pipe is the source of the signals, along with the mains
wires, but
fitting filters to the mains didn't help the problem and I think
its being picked up by the input coils, so whatever is causing the problem
is
perhaps modulating the stray pick up of the RF stations, and
re-transmitting it.
I had a Shimasu telephone answering machine which had a plugpack linear PS

and it managed to cause severe hum interference on any radio used on the
same
house power circuit, despite placing caps to shunt all the supply lines
and mains input
to its PS.
It went into the bin and I now have a tapeless digital answering machine,
which is more reliable, with better audio quality.

Patrick Turner.

Phil B wrote:

Jon,

Wow! Long wish list. You can boil your list down to two requirements:
1. Very low distortion introduced by your ideal tuner.
2. No audio rolloff up to 5kHz.

There have been a number of threads in this group concerning distortion
introduced by the receiver detector stage. Do a Google groups search to
find them.

Most AM tube radios have a pentode vari-mu tube for the IF,
and one end of the coil in the the last IF tuned circuit is connected to a
diode in the pentode
and the other end goes to 100pF, then 47k, then another 100pF, then to the
volume control
which is about 1M or 2M, and you get crackly operation after a couple of
years,
because DC flows in the volume pot.

These simple detector circuits often have the most appalling distortion
which look like cut off distortion, or limiting on one side of the wave
form.

The simplest way to optimise a simple detector is to set it up as follows:-

Retain the existing diode connection of one end of the IF coil.
Retain the existing 100pf-47k-100pf filter.
But connect the output of this filter via a 0.047 uF to the volume control
to
keep the bloomin DC out of the pot, and the crackly vol control should be
quieter,
but maybe it needs replacing if a good internal clean don't fix it.

The crucial next mod is to set up a test signal with nearly 100% modulation
using a
1 kHz audio modulation to generate about -9 volts of AVC voltage.
Then place a 1M test pot across from the first 100pF filter cap to ground,
and adjust the pot for lowest audio distortion.
The surprising thing is that a final value of perhaps 270k is a common value
for
low thd, and the original value used by the maker, ie, the pot, had nothing
to do with
providing the lowest thd.





AM broadcast stations are required to cut off their high audio frequency
abruptly at 5kHz to prevent interference to adjacent channels spaced +
or - 10kHz. You won't find high fidelity among the AM stations no matter
how good your tuner. The best you can hope for is a tuner that doesn't
add it's own frequency response limitations below 5kHz. Do you really
want more than 5KHz response to listen to Rush? (I think a high
frequency limit of, say, 20 Hz would be more appropriate for his show).

Otherwise, I like your Yahoo groups idea. It's a great idea to provide a
forum for discussion of your ideas. It will serve to educate all
participants.

America with 10 kHz station spacing may have this 5 kHz AF limitation,
but my ears tell me that stations here in Oz do have wider audio bandwidth,
despite
being spaced nationally on 9 kHz spaced channels.

I'd guess Oz has fewer stations than America, but our land mass is a similar
area.

Some poor AM tuners insert so much distortion into the recieved signal it
replaces the
missing HF content above 5 kHz, or competes with it if the original
HF content is there. Either way, many AM tuners sound like crap,
especially the three transistor tuners of early solid state.

Patrick Turner.





Phil B

"Jon Noring" wrote in message
...
[New Yahoo Group started: "AM Tube Tuners". See end of this message
for more info.]


In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

(Obviously, a stereo FM tube tuner will be of even more interest to
the tube-o-philes, but there is also a market for an AM tube tuner.
Some may prefer an integrated AM/FM tube tuner, and that's fine, too,
but my focus here is on MW/BCB -- it certainly has special needs
requiring dedicated design even if it is incorporated into an AM/FM
tuner.)

What sort of specs should this AM tuner have? Well, that is certainly
a very open-ended question, with no right answer. However, I believe
the following preliminary list of qualitative specs and requirements
essentially outlines the likely preferred parameter space for the
typical expectations of those who will build and use this AM tube
tuner. Undoubtedly this list is very preliminary, and will be improved
as the experts weigh in (I am NOT an expert on AM tuners), hopefully
even adding real numbers to the resultant specs and requirements.

1) Excellent audio quality at the line-out, effectively reproducing,
with acceptably low distortion, the full fidelity of the broadcast.

(The tuner itself, unlike the radios of yesteryear, will not have
a final audio amplifier stage -- it is assumed the line out will
connect to an audiophile-grade sound system. Low noise is important
since the audiophile system will certainly resolve any noise
present.)

2) Sensitivity, selectivity, etc., will also be quite good, so with an
appropriate antenna, the tuner will be usable for casual MW DXing.

(Obviously it will not, and should not, compete with high-end gear
used for serious MW DXing, such as the Drake R8B and a modded ICOM
R75, to name a couple. But on the other hand, the design should be
"fun" to listen to when the AM band happens to be active at night
-- it should at least be comparable to my venerable RS DX-399 with
RS 15-1853 AM Loop.)

3) The kit/design should be relatively easy (for those experienced
with building audiophile tube amps/pre-amps), and not require a lot
of effort, expertise and new knowledge to construct, align and
adjust, nor require constant adjusting to keep it tuned once built.
The number of tubes in the AM tuner probably should be kept low
(4-6 tubes are preferable by my lay reckoning -- it does help that
there is no final stage audio amplifier.)

(I envision that with the right design, ready-made PCB boards can
be built, like what diytube makes for its amplifiers, for the AM
tube tuner -- to make the design reasonably "fool proof". Obviously
issues not seen in audio amplifiers, such as RF/IF interference,
have to be specially dealt with -- multiple, shielded boards?
Clearly a high-quality AM tuner is a step above audio amplifiers in
complexity and potential problems, but those already skilled in
building tube amps should be able to move to the next level to
assemble the AM tuner and get it working.)

4) The design should specify parts which can be bought new today at
reasonable prices. That means: NO SCROUNGING NEEDED for parts (such
as from old radios on eBay.) Many who will build the AM tuner will
not be old radio collectors, and thus prefer all new, modern parts.
The tubes should be commonly available.

(For example, it appears that multigang tuning capacitors are still
manufactured today by several manufacturers. The components which
require special construction are RF and IF coils. Maybe with a good
design, someone may be able to have a bunch of them made to specs
for use in the kits?)


Strategy and Issues as I see them now:

As noted above, I am clearly not an expert on AM tuners, although I've
been studying whatever resources are available on the Internet,
learning about the designs of yesteryear and those who are trying to
push the envelope with today's better components. Thus, I hope that
the experts here, who have actually built radio tuners and know their
stuff, will take an interest in this. Obviously the first step is to
better state (and later quantify) the requirements and specifications
as attempted above.

However, I can certainly suggest some things which appear important to
discuss (and this list is not prioritized, nor exhaustive), such as:

1) Should we simply find a suitable radio/tuner from yesteryear and
"modernize" it? From the late 30's through the 50's, there are
certainly many worthy candidates to choose from.

Of course, let's begin suggesting candidates!

2) Basic type of receiver. For example, should we consider TRF, or
stick with superheterodyne? TRF, especially using modern components
and modern design, is actually intriguing after reading many of
the messages by John Byrns and others. It potentially can have very
high fidelity audio (from an audiophile sense it is a "purer"
architecture), and does not generate IF interference which again
may turn off audiophiles worried about that. The downsides are
well-known (mainly with selectivity, requiring several carefully
tuned stages to have acceptable selectivity), but there are
workarounds. Superheterodyne is the tried and true receiver type,
with a seemingly endless number of good commercial designs to
choose from. And since simplicity of circuit design is preferred,
would a "supercharged and modernized" AA5 circuit meet the specs?

3) Variable bandwidth control. It appears that a user-adjustable
bandwidth control is called for, especially for switching between
local high-power stations, and weaker distant stations.

4) Antenna input, and antenna gain control? I envision the tuner to
be flexible in the kind of antenna types it will be able to handle.
The types of antennas I've seen used for MW include a ferrite rod,
a simple wire (both can be augmented with, for example, a Radio
Shack AM Loop antenna 15-1853), and more fancy antennas such as
the active loop antennas by Wellbrook (see
http://www.wellbrook.uk.com/products.html#ALA1530 ). I would
assume that an antenna gain control will be needed, but then maybe
not.

5) One problem with building a tuner to cover the MW band is that it
must cover over a 3x span, from about 500khz to 1800khz. This seems
to negatively impact on some receiver designs. Interestingly, has
anyone considered breaking up the BCB band into multiple bands, for
example three bands (500-800, 800-1200, and 1200-1800khz)? Would
doing this confer benefits for some receiver types?

6) Another interesting possibility is that the tuner will almost
exclusively be used to receive commercial broadcasting. In most
of the world, and especially in North America and Europe,
broadcasting is done in very specific frequencies (every 10khz
in the U.S., every 9khz in Europe). So one can envision that
instead of using a multigang tuning capacitor or inductor, to
prewire each channel, specifically tuned for a specific broadcast
frequency -- then have a switch to switch between the channels.
This is especially intriguing for multi-stage TRF designs. Of
course, for the U.S. this would mean over 120 such channels, and I
assume more for Europe. Could get to be unwieldy and calibration
may be an issue -- but then the cost and space of multigang
variable capacitors is significant.

7) A hybrid digital/tube system may be acceptable to the audiophiles.
Any advantages here?

(But there is something to be said for using only components which
are similar to those used in classic radios -- an aesthetic issue
important to some. After all, many well-designed solid state AM
tuners are excellent performers, so restricting ourselves to tubes
is arguably an "aesthetic decision".)


If anyone is interested, I've created a YahooGroup to discuss this
further in a dedicated forum. If you already have a YahooID, you can
subscribe to it via:

http://groups.yahoo.com/group/am-tube-tuners/

If you don't have a YahooID, send a blank email to:



Hope to see you there.


I look forward to your feedback, thoughts, and, yes, candid
criticisms!

Jon Noring

"Jon Noring" a écrit dans le message

...high-performance, tube-based AM (MW/BCB)

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers ...

Audiophile AM is an oxymoron...

Syl

On Tue, 08 Jun 2004 03:04:27 GMT, Jon Noring wrote:

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

No offence Jon, but I think you're nuts. Most hifi listeners (never
mind audiophiles) wouldn't dream of using *FM* for serious listening,
because of the level of optimodding and other sound processing that
goes on. Quite a lot of commercial stations even adjust the playback
speed of their music to make the station sound more 'lively' and to
squeeze in more commercials.

AM has all that, plus very high levels of signal compression and an
effective HF cutoff of about 3.5kHz. You can't improve this by
extending the IF bandwidth, because the stations just don't transmit
anything above this.

There's nothing wrong with building your own high quality AM tuner,
either solid state or tube, but no matter how many gold lettered
Telefunken ECC83s you use it won't sound very good.

Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

Syl's Old Radioz wrote:

"Jon Noring" a écrit dans le message

...high-performance, tube-based AM (MW/BCB)

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers ...

Audiophile AM is an oxymoron...

Syl

If the audio on a CD is not all used to modulate the AM carrier,
it could be said it ain't hi-fi, and 5 kHz bandwidth or less is
certainly not hi-fi.
But there is reason for those who build gear for the fun to try
to make the receiver as good as possible.
If 5 kHz is all we get, all the more reason to reduce thd to a minimum.

FM only goes to 16 kHz, and the audio information to
get the difference between L and R channels is contained on a
subcarrier signal of 38 kHz.

Unfortunately, our predecessors thought 16 kHz was plenty bandwidth.
It would have been nicer to have 20 kHz, and a 70 kHz subcarrier,
but then you couldn't have so many subcarriers as we do now,
which is one at 38 kHz, then another at 76 kHz, and another at 96 kHz,
so that several extra information channels can be carried on the one
signal transmitted between 88 and 108 mHz.

Fidelity was always going to suffer from the forseeable desire for
channels.

The AM mid wave band radio spectrum could have a lot more fidelity if we
had stations
separated by 40 kHz instead of 10 kHz. But commercial interests were
always going to
put fidelity last, and profits first.

Now there's talk of digital broadcast, and the phasing out of FM and AM
broadcasting.
But I don't expect it to dissappear soon, and even more channels for
people's attention seem
to spring up daily to consume the leisure time of the masses,
and TV gets the main share.
Digital recievers need to be costed below the existing radio receiver
costs before
folks will buy them as an add on for their TV watching.
People's expectations about home entertainment are far beyond
just sitting down listening to music.
Most AM is listened to in cars, if at all, but usually while folks are
doing something else.
There will always be broadcasting of some sort, because its possible,
and the spectrum exists, but the programme quality decline continues.
As fewer listeners tune in, there are less advertisers willing to pay
the stations,
and its not worthwhile building a super dooper radio to listen to them.

I have 3 HRO receivers in parts from which I plan to get two good ones,
I have several other radio projects to do, but alas no time, since I
have to work for
a living.

I'd like to try using a 2 MHz IF strip for my A radio, because at least
there
3 stations here worth listening to out of the total of 7.

I figure the 2 MHz IF frequency would allow
a Q of 50 for each LC circuit, and thus the BW would be 40 kHz for each,

so with 4 or 6 consecutive LC circuits the BW could be 20 kHz,
thus allowing 10 kHz of audio BW.
Perhaps single tuned IF coils are all that's needed.
The single tuned high Q IF auto tranny is pretty awful at 455 kHz, as
used in transistor
based circuits because with a Q of 100, the BW is only 4.55 kHz,
and with two such coils you have only say 3.6 kHz, so only 1.8 kHz of
audio can
pass, and many transistor radios have only 1.8 kHz of audio BW.
Some tube types only have that much. I have measured plenty
of impressive looking tube sets with RF stages, and the total number of
tuned circuits is
about 6 including 4 IF coils, and the bandwidth narrows down badly.

Communications radios sometimes used lower IF at say 100 kHz
to take advantage of the lower bandwidth for a given Q.
This allowed very good selectivity for short wave,
but was hopeless for local station AM.

Its possible that by removing many turns off existing 455 kHz IFTs,
the 2MHz could be achieved.

The oscilator would operate at the BCB frequencies + 2 MHZ.
So the oscillator coils and circuit would need revision, but then that'd
be easy,
since the coils do not differ much from the usual low end short wave
types.

The other way of doing an AM radio today is to use totally digital
techniques for converting what is coming from the antenna and pull out
the audio from
any wanted station in ways which nobody in 1935 could ever have
imagined.
I think this would be an interesting digital project for someone.

Everyone has a PC at home these days, and it sould be easy to
use it to sift out a few radio waves.

But if fidelity isn't transmitted, not even a PC can decide correctly
what to substitute for missing audio HF.


Just my 3c worth,

Patrick Turner.

Syl wrote:
Jon Noring wrote:

...high-performance, tube-based AM (MW/BCB)

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers ...

Audiophile AM is an oxymoron...

Yes, in a sense this is true if we look at it from the broadcast side
of things.

However, if an audiophile wants to add an AM tuner to their system
(such as listen to oldies, news, sports, talk radio, whatever), they
*want* to hear the broadcasts at the highest possible audio fidelity
of whatever is carried by the signal. (TRF looks especially intriguing
for the AM tuner design, which I hope John Byrns will comment on.)

Definitely, the AM tuner design must not get in the way. As Patrick
Turner noted, in Australia may of the broadcasters appear to take
advantage of having fewer stations and broadcast with higher audio
bandwidth (even though channel spacing is 9khz), so the AM tuner
should have the ability to handle that higher audio bandwidth and do a
great job at it. Variable bandwidth control is certainly indicated
(especially if the tuner will also be used for casual DXing, where the
bandwidth will need to be narrowed for resolving real weak stations.)

About volume control (as also noted by Patrick Turner), I'm not sure
if the AM tuner will need one if connected to a preamp. If it is to
connect directly to an amplifier, though, it will need a volume
control. Here, putting a "standard" passive preamp volume control at
the line out of the AM tuner is indicated, unless there is a reason
to place the volume control further upstream in the "chain."

Jon Noring


p.s., do join the YahooGroup 'am-tube-tuners' if this topic interests
you. If you already have a YahooID, you can subscribe to it via:

http://groups.yahoo.com/group/am-tube-tuners/

If you don't have a YahooID, send a blank email to:

Paul Sherwin wrote:

On Tue, 08 Jun 2004 03:04:27 GMT, Jon Noring wrote:

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

No offence Jon, but I think you're nuts. Most hifi listeners (never
mind audiophiles) wouldn't dream of using *FM* for serious listening,
because of the level of optimodding and other sound processing that
goes on. Quite a lot of commercial stations even adjust the playback
speed of their music to make the station sound more 'lively' and to
squeeze in more commercials.

All the audiophiles I know do listen fervently to the FM stations we have
which
take pains to transmit unadulterated audio.
Where I am is a city of only 300,000, and we have
an Arts FM station funded by subcribers and mild advertisers, and their
signal is tops.
The govt owned station, ABC Classic FM broadcasts nothing but
classical and some jazz. Electric guitars are rarely heard.
They regularly do live broadcasts each sunday and during the week,
and all are at a high technical standard.
Then we have a community FM radio station run by feminists
and mainly leftists, and that has the best specialist rythym and blues
shows.
Then there is a station for ethnic culturists.

The remaining stations are pop music, christian, or sports report based,
and thir
programmes are all just ****e to me, and the audio is little better than
the AM stations,
and I am allergic to ALL their adverts, which have the opposite effect on
me that the advertisers hope for,
ie, I WILL NOT buy coca cola after hearing an add saying things go better
with coke.


AM has all that, plus very high levels of signal compression and an
effective HF cutoff of about 3.5kHz. You can't improve this by
extending the IF bandwidth, because the stations just don't transmit
anything above this.

Here in Oz, they do transmit more than 3.5 kHz of audio,
so we get some stations worth listening to.

There's nothing wrong with building your own high quality AM tuner,
either solid state or tube, but no matter how many gold lettered
Telefunken ECC83s you use it won't sound very good.

There are programs where the content has little above 8 kHz.
If one stretches the BW of the receiver here in Oz,
its surprising how good AM radio can sound.

A Telefunken ECC83 is a useless tube in any RF circuit.
I get your point, but ppl in r.a.t are spread around the globe
where different conditions prevail.

Patrick Turner.



Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

Paul Sherwin wrote:
Jon Noring wrote:

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built
by hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

No offence Jon, but I think you're nuts.

No offense is taken, and yes I may be a little nuts. :^)


Most hifi listeners (never mind audiophiles) wouldn't dream of using
*FM* for serious listening, because of the level of optimodding and
other sound processing that goes on. Quite a lot of commercial
stations even adjust the playback speed of their music to make the
station sound more 'lively' and to squeeze in more commercials.

Nevertheless, there are those hifi/audiophile listeners, such as
myself, who still wish to connect both AM and FM tuners to their audio
system, to listen to various broadcasts. Not everything audio is found
on CD/vinyl.

On FM, especially among alternative FM stations, one often finds very
unusual musical programs being broadcast of music which the listener
does not have in their collection (it helps them to expand their
horizons and maybe go out and purchase said music on CD/vinyl.) In
addition, there are sometimes live broadcasts of concerts which will
never appear on CD/vinyl. (In Salt Lake City, the alternative FM
station I am thinking of is KRCL, http://www.krcl.org/ . Really a fun
station to listen to, especially the late Sunday night program
broadcasting 1920's to 1940's era recordings.)

On AM there are certainly broadcasts which interest different people
for different reasons at different times. Live sports events not found
elsewhere, news, of course the venerable talk radio, and for some of
us, we like to spin the dial at night and see what distant stations we
can pull in.

Thus, if we do connect AM and FM tuners to our system, we want the
tuners to deliver the highest audio quality signal to our amplifiers.
That is, the tuners should not taint the broadcast signal any more
than it already is tainted as it leaves the broadcaster's antenna.

(Btw, aren't there alternative FM stations which do not play these
games of distorting the sound, and only broadcast the purest possible
signal?)


AM has all that, plus very high levels of signal compression and an
effective HF cutoff of about 3.5kHz. You can't improve this by
extending the IF bandwidth, because the stations just don't transmit
anything above this.

Well, maybe in the U.S. most stations cutoff at 3.5khz. Then that's
where they cutoff. However, the AM tuner design is intended for the
world, and as Patrick Turner noted, in Australia many broadcasters
have a much higher rolloff because of the "open highway" they have
on the BCB -- fewer stations spread farther apart.


There's nothing wrong with building your own high quality AM tuner,
either solid state or tube, but no matter how many gold lettered
Telefunken ECC83s you use it won't sound very good.

Agreed in principle. The AM tuner must deliver the highest possible
fidelity as broadcast, that's all. It must have very low distortion.

One question to ask is in various areas of the world (including the
U.S.) what is the distribution of HF cutoff among the many broadcast
stations? I doubt in the U.S. every broadcaster rolls off HF at
3.5khz, but maybe most do -- are there any AM stations in the U.S.
which have a much higher HF rolloff than 3.5khz? Note again Patrick's
comment on Australian AM broadcasters.

Jon Noring

Patrick Turner wrote:


Its possible that by removing many turns off existing 455 kHz IFTs,
the 2MHz could be achieved.

The oscilator would operate at the BCB frequencies + 2 MHZ.
So the oscillator coils and circuit would need revision, but then that'd
be easy,
since the coils do not differ much from the usual low end short wave
types.



A good set of ~2.8 MC IF transformers can be had in the 6-9.1 MC ARC-5
receivers.


Jeff Goldsmith

Phil B wrote:

Jon,

Wow! Long wish list. You can boil your list down to two requirements:
1. Very low distortion introduced by your ideal tuner.
2. No audio rolloff up to 5kHz.

There have been a number of threads in this group concerning distortion
introduced by the receiver detector stage. Do a Google groups search to
find them.

AM broadcast stations are required to cut off their high audio frequency
abruptly at 5kHz to prevent interference to adjacent channels spaced +
or - 10kHz. You won't find high fidelity among the AM stations no matter
how good your tuner. The best you can hope for is a tuner that doesn't
add it's own frequency response limitations below 5kHz. Do you really
want more than 5KHz response to listen to Rush?

I was about to argue here until I realized you were talking about the "right
wing wacko", as Tom Leykis would say, and not the progressive rock band ;)

As for the tuner... try the TRF which is in some RCA tube manuals... it uses
a 12AU7 and some rectifier, I believe. There's also the Heathkit AM tuner
which was made in the 50s, and may be worth copying. Some people have also
had excellent luck with a "crystal" radio - I believe AES sells a kit which
is intended for hi-fi AM use, and again, one was sold in the 50s.

(I think a high
frequency limit of, say, 20 Hz would be more appropriate for his show).

Otherwise, I like your Yahoo groups idea. It's a great idea to provide a
forum for discussion of your ideas. It will serve to educate all
participants.

Phil B

"Jon Noring" wrote in message
...
[New Yahoo Group started: "AM Tube Tuners". See end of this message
for more info.]


In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built by
hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

(Obviously, a stereo FM tube tuner will be of even more interest to
the tube-o-philes, but there is also a market for an AM tube tuner.
Some may prefer an integrated AM/FM tube tuner, and that's fine, too,
but my focus here is on MW/BCB -- it certainly has special needs
requiring dedicated design even if it is incorporated into an AM/FM
tuner.)

What sort of specs should this AM tuner have? Well, that is certainly
a very open-ended question, with no right answer. However, I believe
the following preliminary list of qualitative specs and requirements
essentially outlines the likely preferred parameter space for the
typical expectations of those who will build and use this AM tube
tuner. Undoubtedly this list is very preliminary, and will be improved
as the experts weigh in (I am NOT an expert on AM tuners), hopefully
even adding real numbers to the resultant specs and requirements.

1) Excellent audio quality at the line-out, effectively reproducing,
with acceptably low distortion, the full fidelity of the broadcast.

(The tuner itself, unlike the radios of yesteryear, will not have
a final audio amplifier stage -- it is assumed the line out will
connect to an audiophile-grade sound system. Low noise is important
since the audiophile system will certainly resolve any noise
present.)

2) Sensitivity, selectivity, etc., will also be quite good, so with an
appropriate antenna, the tuner will be usable for casual MW DXing.

(Obviously it will not, and should not, compete with high-end gear
used for serious MW DXing, such as the Drake R8B and a modded ICOM
R75, to name a couple. But on the other hand, the design should be
"fun" to listen to when the AM band happens to be active at night
-- it should at least be comparable to my venerable RS DX-399 with
RS 15-1853 AM Loop.)

3) The kit/design should be relatively easy (for those experienced
with building audiophile tube amps/pre-amps), and not require a lot
of effort, expertise and new knowledge to construct, align and
adjust, nor require constant adjusting to keep it tuned once built.
The number of tubes in the AM tuner probably should be kept low
(4-6 tubes are preferable by my lay reckoning -- it does help that
there is no final stage audio amplifier.)

(I envision that with the right design, ready-made PCB boards can
be built, like what diytube makes for its amplifiers, for the AM
tube tuner -- to make the design reasonably "fool proof". Obviously
issues not seen in audio amplifiers, such as RF/IF interference,
have to be specially dealt with -- multiple, shielded boards?
Clearly a high-quality AM tuner is a step above audio amplifiers in
complexity and potential problems, but those already skilled in
building tube amps should be able to move to the next level to
assemble the AM tuner and get it working.)

4) The design should specify parts which can be bought new today at
reasonable prices. That means: NO SCROUNGING NEEDED for parts (such
as from old radios on eBay.) Many who will build the AM tuner will
not be old radio collectors, and thus prefer all new, modern parts.
The tubes should be commonly available.

(For example, it appears that multigang tuning capacitors are still
manufactured today by several manufacturers. The components which
require special construction are RF and IF coils. Maybe with a good
design, someone may be able to have a bunch of them made to specs
for use in the kits?)


Strategy and Issues as I see them now:

As noted above, I am clearly not an expert on AM tuners, although I've
been studying whatever resources are available on the Internet,
learning about the designs of yesteryear and those who are trying to
push the envelope with today's better components. Thus, I hope that
the experts here, who have actually built radio tuners and know their
stuff, will take an interest in this. Obviously the first step is to
better state (and later quantify) the requirements and specifications
as attempted above.

However, I can certainly suggest some things which appear important to
discuss (and this list is not prioritized, nor exhaustive), such as:

1) Should we simply find a suitable radio/tuner from yesteryear and
"modernize" it? From the late 30's through the 50's, there are
certainly many worthy candidates to choose from.

Of course, let's begin suggesting candidates!

2) Basic type of receiver. For example, should we consider TRF, or
stick with superheterodyne? TRF, especially using modern components
and modern design, is actually intriguing after reading many of
the messages by John Byrns and others. It potentially can have very
high fidelity audio (from an audiophile sense it is a "purer"
architecture), and does not generate IF interference which again
may turn off audiophiles worried about that. The downsides are
well-known (mainly with selectivity, requiring several carefully
tuned stages to have acceptable selectivity), but there are
workarounds. Superheterodyne is the tried and true receiver type,
with a seemingly endless number of good commercial designs to
choose from. And since simplicity of circuit design is preferred,
would a "supercharged and modernized" AA5 circuit meet the specs?

3) Variable bandwidth control. It appears that a user-adjustable
bandwidth control is called for, especially for switching between
local high-power stations, and weaker distant stations.

4) Antenna input, and antenna gain control? I envision the tuner to
be flexible in the kind of antenna types it will be able to handle.
The types of antennas I've seen used for MW include a ferrite rod,
a simple wire (both can be augmented with, for example, a Radio
Shack AM Loop antenna 15-1853), and more fancy antennas such as
the active loop antennas by Wellbrook (see
http://www.wellbrook.uk.com/products.html#ALA1530 ). I would
assume that an antenna gain control will be needed, but then maybe
not.

5) One problem with building a tuner to cover the MW band is that it
must cover over a 3x span, from about 500khz to 1800khz. This seems
to negatively impact on some receiver designs. Interestingly, has
anyone considered breaking up the BCB band into multiple bands, for
example three bands (500-800, 800-1200, and 1200-1800khz)? Would
doing this confer benefits for some receiver types?

6) Another interesting possibility is that the tuner will almost
exclusively be used to receive commercial broadcasting. In most
of the world, and especially in North America and Europe,
broadcasting is done in very specific frequencies (every 10khz
in the U.S., every 9khz in Europe). So one can envision that
instead of using a multigang tuning capacitor or inductor, to
prewire each channel, specifically tuned for a specific broadcast
frequency -- then have a switch to switch between the channels.
This is especially intriguing for multi-stage TRF designs. Of
course, for the U.S. this would mean over 120 such channels, and I
assume more for Europe. Could get to be unwieldy and calibration
may be an issue -- but then the cost and space of multigang
variable capacitors is significant.

7) A hybrid digital/tube system may be acceptable to the audiophiles.
Any advantages here?

(But there is something to be said for using only components which
are similar to those used in classic radios -- an aesthetic issue
important to some. After all, many well-designed solid state AM
tuners are excellent performers, so restricting ourselves to tubes
is arguably an "aesthetic decision".)


If anyone is interested, I've created a YahooGroup to discuss this
further in a dedicated forum. If you already have a YahooID, you can
subscribe to it via:

http://groups.yahoo.com/group/am-tube-tuners/

If you don't have a YahooID, send a blank email to:



Hope to see you there.


I look forward to your feedback, thoughts, and, yes, candid
criticisms!

Jon Noring

"Jon Noring" wrote in message
...
[New Yahoo Group started: "AM Tube Tuners". See end of this message
for more info.]


In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

[snip]

Does anybody broadcast true hi-fi AM anymore? The FCC limits the total
bandwidth to 20 kHz or an audio bandwidth of 10 kHz but I think most
broadcasters don't even go that far. More than that, nearly all the
broadcasters now seem to be pre-emphisising the trebles, and AM usually
sounds shrill on a wide bandwidth radio. I assume they do this to somewhat
compensate for the normal IF roll off in a typical radio. Add in the other
audio processing that broadcasters use, and AM doesn't really sound a whole
lot better on a wide band radio.

I did hear some classical music on a local ethnic station a few weeks ago
which sounded quite good. It actually had some dynamic range and the
station is one of the few which sounds like they use their full bandwidth.

Getting wideband IF transformers will be a real problem. I don't know of
any NOS sources for them.

Frank Dresser

"Phil B" wrote in message
...

AM broadcast stations are required to cut off their high audio frequency
abruptly at 5kHz to prevent interference to adjacent channels spaced +
or - 10kHz.


I've read articles which claim there was no specific limit on AM audio
bandwidth, but the FCC required the stations to limit bandwidth to limit
interference. Given the normal minimum station spacing of 30 kHz in a given
area, this would imply a maximum audio bandwidth of 15 kHz. If sideband
splatter is any indication, I know the old rocker WCFL at 1000 kHz would
splat out the lower sideband of KDKA at 1020 kHz in the Chicago area. Now,
KDKA is an easy nightthime catch.

As stations were added to markets, the FCC limited the audio bandwidth to 10
kHz.

I've read textbooks which claim a maximum allowed 5 kHz audio bandwidth but
I don't trust the textbooks, so I searched the FCC website.

I came up with:

3. Sound Broadcasting

Sound broadcasting, double-sideband..

BINFn/INF=2M, M may vary between 4000 and 10000
depending on the quality desired

This defination was among a group above the FCC's formulas:

BINFn/INF = Necessary bandwidth in hertz

So, if I'm reading this correctly, the necessary bandwidth for standard AM
will be twice the audio bandwidth, which must be between a minimum audio
bandwidth of 4000 Hz and a maximum audio bandwidth of 10,000Hz.

This is from:

http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=2&SECTION=202&YEAR=2001&TYPE =TEXT

Frank Dresser

Patrick Turner wrote in message ...
Syl's Old Radioz wrote:

"Jon Noring" a écrit dans le message

...high-performance, tube-based AM (MW/BCB)

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers ...

Audiophile AM is an oxymoron...

Syl
Now there's talk of digital broadcast, and the phasing out of FM and AM
broadcasting.
But I don't expect it to dissappear soon, and even more channels for
people's attention seem
to spring up daily to consume the leisure time of the masses,
and TV gets the main share.
Digital recievers need to be costed below the existing radio receiver
costs before
folks will buy them as an add on for their TV watching.
People's expectations about home entertainment are far beyond
just sitting down listening to music.
Most AM is listened to in cars, if at all, but usually while folks are
doing something else.
There will always be broadcasting of some sort, because its possible,
and the spectrum exists, but the programme quality decline continues.
As fewer listeners tune in, there are less advertisers willing to pay
the stations,
and its not worthwhile building a super dooper radio to listen to them.

I have 3 HRO receivers in parts from which I plan to get two good ones,
I have several other radio projects to do, but alas no time, since I
have to work for
a living.

I'd like to try using a 2 MHz IF strip for my A radio, because at least
there
3 stations here worth listening to out of the total of 7.

I figure the 2 MHz IF frequency would allow
a Q of 50 for each LC circuit, and thus the BW would be 40 kHz for each,

so with 4 or 6 consecutive LC circuits the BW could be 20 kHz,
thus allowing 10 kHz of audio BW.
Perhaps single tuned IF coils are all that's needed.
The single tuned high Q IF auto tranny is pretty awful at 455 kHz, as
used in transistor
based circuits because with a Q of 100, the BW is only 4.55 kHz,
and with two such coils you have only say 3.6 kHz, so only 1.8 kHz of
audio can
pass, and many transistor radios have only 1.8 kHz of audio BW.
Some tube types only have that much. I have measured plenty
of impressive looking tube sets with RF stages, and the total number of
tuned circuits is
about 6 including 4 IF coils, and the bandwidth narrows down badly.

Communications radios sometimes used lower IF at say 100 kHz
to take advantage of the lower bandwidth for a given Q.
This allowed very good selectivity for short wave,
but was hopeless for local station AM.

Its possible that by removing many turns off existing 455 kHz IFTs,
the 2MHz could be achieved.

The oscilator would operate at the BCB frequencies + 2 MHZ.
So the oscillator coils and circuit would need revision, but then that'd
be easy,
since the coils do not differ much from the usual low end short wave
types.

The other way of doing an AM radio today is to use totally digital
techniques for converting what is coming from the antenna and pull out
the audio from
any wanted station in ways which nobody in 1935 could ever have
imagined.
I think this would be an interesting digital project for someone.

Everyone has a PC at home these days, and it sould be easy to
use it to sift out a few radio waves.

But if fidelity isn't transmitted, not even a PC can decide correctly
what to substitute for missing audio HF.


Just my 3c worth,

Patrick Turner.

I don't have 3c and I only have 2GB. WTF do I want to do that on this
POS. Why does 'radio' have to be done on a computer? Get moving and
build a dedicated device (radio) instead of using a damned computer.
This should be in a sci. group.

So, if I'm reading this correctly, the necessary bandwidth for standard AM
will be twice the audio bandwidth, which must be between a minimum audio
bandwidth of 4000 Hz and a maximum audio bandwidth of 10,000Hz.



Contrary to popular belief, AM stations broadcast with a bandwidth of
20KHz, which
makes for audio up to 10KHz. This much bandwidth in a tuner works well
for local stations,
but for DX work you'd want to cut your bandwidth in your receiver to
+-5KHz to avoid
excessive splatter. Even then, you'll still get some "monkey chatter"
from an adjacent channel
station. "Monkey chatter" is a technical term for the modulated audio
that came from station
A showing up "upside down" when you are listening to station B, 10KHz
away on the dial.
"Upside down" meaning that an audio tone of 9KHz station A transmitted
gets demodulated
by your radio when it's tuned to station B, as a 1Khz tone. 9.5Khz -
500Hz, and so on.
Human speach "inverted" this way sounds like "monkey chatter". The only
way to reduce
monkey chatter is to null out station A with the loop antenna. But if
there's another station C
10KHz on the other side of the desired station, and not in the same
direction of the first
undesired station, you're sunk.

You'll also want a sharp 10KHz notch filter (9Khz in Europe and
Australia and elsewhere).
That's to get rid of the heterodyne from the adjacent stations' carriers.

If you can find a copy of RDH4 (Radio Designer's Handbook edition 4), it has
lots of info on radio receiver design. But it assumes that you have a
working
knowledge of electrical engineering. That is, not a beginner's book.

Does anybody broadcast true hi-fi AM anymore? The FCC limits the total
bandwidth to 20 kHz or an audio bandwidth of 10 kHz but I think most
broadcasters don't even go that far. More than that, nearly all the
broadcasters now seem to be pre-emphisising the trebles, and AM usually
sounds shrill on a wide bandwidth radio. I assume they do this to somewhat
compensate for the normal IF roll off in a typical radio. Add in the other
audio processing that broadcasters use, and AM doesn't really sound a whole
lot better on a wide band radio.


snip

Getting wideband IF transformers will be a real problem. I don't know of
any NOS sources for them.


A bunch of approaches exist.

In the 50s and 60s, several RF suppliers-I get Miller and Millen
confused,one at least-offered sets of cans to build, essentially,
crystal radios that you hooked up to your hi-fi preamp. They still had
high-gain inputs without RIAA for 78s in those days, I presume. This
was considered the best possible way to demod AM. I don't know how
well it would work with the crapped-up bands and disinclination to run
long wire antennas and real RF grounds today.

Later on, Klipsch dealers would have a similar set built on a display
board hooked to a matching xfmr which they would hook to a K-horn.
With no power supply or amplifying devices, if you were within a few
miles of a 50-kw station-or if you were in a very quiet room with a
big longwire and really good ground, even at night or in the sticks-
you had a surprisingly loud and clear audio feed. I can very clearly
remember hearing Simon and Garfunkel's "The Sound of Silence" for the
first time on this arrangement. When did that come out? Late 60s I'm
guessing.

Before that even, people in the 30s' (or so they say...) would modify
old A****er Kents into tuners by removing the output section and
providing a B+ and filament supply and furnishing an amp and speaker.
Camera repair guru Ed Romney, who has since went to the big
transmitter shack, talks of this in his radio repair book. He may have
even reprinted the article: I know I had ordered one on interlibrary
loan back in the 80s. Consumer Reports recommended this as an
alternative to the E.H. Scotts and Philharmonics of the day.

Finally, unless you really like heterodyne whistles, you will want a
10 kHz notch filter, or a rolloff.

But if fidelity isn't transmitted, not even a PC can decide correctly
what to substitute for missing audio HF.


Just my 3c worth,

Patrick Turner.

I don't have 3c and I only have 2GB. WTF do I want to do that on this
POS. Why does 'radio' have to be done on a computer? Get moving and
build a dedicated device (radio) instead of using a damned computer.
This should be in a sci. group.

I don't expect anyone to pay 3c for what I say, which could be seen as OT.

I have already built a decent AM radio, and re-engineered an FM radio,
both to my own designs, so I feel OK about considering the alternatives
which might involve a PC.

Patrick Turner.

Robert Casey wrote:




So, if I'm reading this correctly, the necessary bandwidth for standard AM
will be twice the audio bandwidth, which must be between a minimum audio
bandwidth of 4000 Hz and a maximum audio bandwidth of 10,000Hz.



Contrary to popular belief, AM stations broadcast with a bandwidth of
20KHz, which
makes for audio up to 10KHz. This much bandwidth in a tuner works well
for local stations,
but for DX work you'd want to cut your bandwidth in your receiver to
+-5KHz to avoid
excessive splatter. Even then, you'll still get some "monkey chatter"
from an adjacent channel
station. "Monkey chatter" is a technical term for the modulated audio
that came from station
A showing up "upside down" when you are listening to station B, 10KHz
away on the dial.
"Upside down" meaning that an audio tone of 9KHz station A transmitted
gets demodulated
by your radio when it's tuned to station B, as a 1Khz tone. 9.5Khz -
500Hz, and so on.
Human speach "inverted" this way sounds like "monkey chatter". The only
way to reduce
monkey chatter is to null out station A with the loop antenna. But if
there's another station C
10KHz on the other side of the desired station, and not in the same
direction of the first
undesired station, you're sunk.

What you are saying here is true about monkey chatter,
and "inversion" of music and speach.
But usually it only applies to distance listening.

And a sharp bridged T LC notch notch filter won't reduce the monkey
chatter, just the 9/10kHz whistle from carriers interfering.



You'll also want a sharp 10KHz notch filter (9Khz in Europe and
Australia and elsewhere).
That's to get rid of the heterodyne from the adjacent stations' carriers.

If you can find a copy of RDH4 (Radio Designer's Handbook edition 4), it has
lots of info on radio receiver design. But it assumes that you have a
working
knowledge of electrical engineering. That is, not a beginner's book.

Well said, the RDH4 isn't easy to read. But each sentence is never a waste of
words,
so you must consider each word you read.

Building radios the way they did in 1955 from nothing upwards using a few tubes
takes a lot of effort, and the main thing apart from knowledge that makes 95% of
ppl
abandon projects is the building of coils and the discipline about
constructional quality.

Patrick Turner.

Steven Dinius wrote:
Brian wrote:

10 kHz is the high-frequency limit in the USA.

I have several tube radios and the AM sounds nice enough with clean
higher frequencies and a couple with nice bass. As to why the OP wants
a tuner escapes me. To me the point of an AA-5 or AA-6 is that you can
get a decent audio amp and good power with those same tubes, put them
in a nice cabinet with a good speaker and REALLY ENJOY it. What's the
point? I thought that I buy all these different radios for the reason
that they have UNIQUE qualities and personalities. For the most part,
I have not had to modify a tube set other than the speaker for my
floor console, as they all have been satisfactory unlike some of the
SS stuff I have.

Well, being the "OP", I want a high-audio performance, modern design
AM tuner to integrate into my audio system -- and I believe a lot of
tube-o-philes likewise want that -- but not everyone obviously. There
are several reasons why most higher-grade audio systems use separate
components, the reasons of which are obvious to most everyone. The AM
tuner is no different than other audio components in this regard.

Even though it may seem strange to die-hard old radio collectors the
desire to have a modern-design and built AM tube tuner ("there are so
many old ones out there, why build one from scratch?"), it is equally
strange to those who want such an AM tuner (to integrate into their
audio system) to be told they should quit wanting what they want and
just find some old radio and restore it for their listening purposes,
and forget about integrating it into their audio system.

Both viewpoints are neither strange nor wrong -- both are looking at
things from different perspectives and goals: radio collectors are
more interested in old radios as "works of art" (where art is both in
design and electronic function), while those who want an AM tube tuner
are more interested in actual listening to contemporary broadcasts
(such as they are!), and still want to have the "tube sound": the
aesthetics and allure of the tube.

(In some regards, the tube-o-philes are not much different than old
radio collectors. The former love the aesthetics of the "tube" for
audio listening purposes; the latter love the aesthetics of the old
radios in and of themselves -- as works of the technical and visual
arts. Both are valid ways of looking at the big world of radio. Of
course, there is a third group who are totally utilitarian and prefer
to focus on building the high-performance AM tuner using completely
DSP/solid state design, and to hell with tubes and wood/bakelite
cabinets. That's also a valid perspective -- and probably makes for
the ultimate design.)

Anyway, if someone so chooses, they can take the modern AM tube tuner
design and connect a preamp/amp to it and integrate that into a single
cabinet with a speaker, to make a stand-alone radio. The cabinet could
either come from some old 1930's cabinet (where the chassis is missing
or unrestorable), or be designed from scratch to be reminiscent of a
classic late 1930's radio (maybe by combining the best features of
several highly regarded radio cabinets of the period). The latter
could make for a fun project for those so inclined and skilled. I've
even sketched out in my mind the design for such a cabinet -- I'm not
sure if I'll ever build it, but it looms in my mind ... a combination
of the old with the new. Of course, most radio collectors are now
probably aghast at my heretical thoughts. smile /

*****

On a different subtopic, Bob Casey sent me a recording made from an
AM radio broadcast (a local ABC station) using his home-built TRF
design receiver. He may have announced this recording to one or more
of these newsgroups in the past -- I don't know -- a check on Google
did not bring anything up. It has amazing sound, very FM-like (very
clean with low distortion), and it is obvious the broadcaster (I think
it is WABC) used a rolloff much higher than the "typical" 3.5khz being
bandied about here.

From my studying of what I can find on Google web sites and newsgroup
postings on AM receiver design, I believe the prime candidate for the
high-performance, modern-design AM tube tuner is a TRF design of some
sort, not a superheterodyne. The major issue appears to be how to get
the multiple stages (three stages appear necessary to attain
appropriate sensitivity and selectivity) all in "synch" (term used
loosely) for a given radio frequency.

Of course, thinking outside the box as I am wont of doing, I first of
all notice that the AM tuner will be used for commercial broadcasts
which are on strictly assigned frequencies: every 10khz in the U.S.
and every 9khz in Europe and elsewhere. If so, could we not dispense
with infinitely variable tuning and take a channel approach (like tv
receivers of old)? For TRF designs, this may be what is needed to
"perfectly synch" the three or more multiple stages, and do so in ways
not possible with the "1-D" restriction of a multiganged air tuning
capacitor (or variable inductor.) This may allow varying more
components for each channel to get the "perfect" fit between the
stages.

Anyway, I'll leave it to the experts to mull over the channel
approach to an AM tube tuner, to see if it will actually confer any
real advantages (especially for TRF circuits), and if so, how to
implement it in a practical sense (I have ideas), how to deal with
interference issues, etc.

Jon Noring

Jon Noring wrote:

Steven Dinius wrote:
Brian wrote:

10 kHz is the high-frequency limit in the USA.

I have several tube radios and the AM sounds nice enough with clean
higher frequencies and a couple with nice bass. As to why the OP wants
a tuner escapes me. To me the point of an AA-5 or AA-6 is that you can
get a decent audio amp and good power with those same tubes, put them
in a nice cabinet with a good speaker and REALLY ENJOY it. What's the
point? I thought that I buy all these different radios for the reason
that they have UNIQUE qualities and personalities. For the most part,
I have not had to modify a tube set other than the speaker for my
floor console, as they all have been satisfactory unlike some of the
SS stuff I have.

Well, being the "OP", I want a high-audio performance, modern design
AM tuner to integrate into my audio system -- and I believe a lot of
tube-o-philes likewise want that -- but not everyone obviously. There
are several reasons why most higher-grade audio systems use separate
components, the reasons of which are obvious to most everyone. The AM
tuner is no different than other audio components in this regard.

Even though it may seem strange to die-hard old radio collectors the
desire to have a modern-design and built AM tube tuner ("there are so
many old ones out there, why build one from scratch?"), it is equally
strange to those who want such an AM tuner (to integrate into their
audio system) to be told they should quit wanting what they want and
just find some old radio and restore it for their listening purposes,
and forget about integrating it into their audio system.

Both viewpoints are neither strange nor wrong -- both are looking at
things from different perspectives and goals: radio collectors are
more interested in old radios as "works of art" (where art is both in
design and electronic function), while those who want an AM tube tuner
are more interested in actual listening to contemporary broadcasts
(such as they are!), and still want to have the "tube sound": the
aesthetics and allure of the tube.

(In some regards, the tube-o-philes are not much different than old
radio collectors. The former love the aesthetics of the "tube" for
audio listening purposes; the latter love the aesthetics of the old
radios in and of themselves -- as works of the technical and visual
arts. Both are valid ways of looking at the big world of radio. Of
course, there is a third group who are totally utilitarian and prefer
to focus on building the high-performance AM tuner using completely
DSP/solid state design, and to hell with tubes and wood/bakelite
cabinets. That's also a valid perspective -- and probably makes for
the ultimate design.)

Anyway, if someone so chooses, they can take the modern AM tube tuner
design and connect a preamp/amp to it and integrate that into a single
cabinet with a speaker, to make a stand-alone radio. The cabinet could
either come from some old 1930's cabinet (where the chassis is missing
or unrestorable), or be designed from scratch to be reminiscent of a
classic late 1930's radio (maybe by combining the best features of
several highly regarded radio cabinets of the period). The latter
could make for a fun project for those so inclined and skilled. I've
even sketched out in my mind the design for such a cabinet -- I'm not
sure if I'll ever build it, but it looms in my mind ... a combination
of the old with the new. Of course, most radio collectors are now
probably aghast at my heretical thoughts. smile /

*****

On a different subtopic, Bob Casey sent me a recording made from an
AM radio broadcast (a local ABC station) using his home-built TRF
design receiver. He may have announced this recording to one or more
of these newsgroups in the past -- I don't know -- a check on Google
did not bring anything up. It has amazing sound, very FM-like (very
clean with low distortion), and it is obvious the broadcaster (I think
it is WABC) used a rolloff much higher than the "typical" 3.5khz being
bandied about here.

From my studying of what I can find on Google web sites and newsgroup
postings on AM receiver design, I believe the prime candidate for the
high-performance, modern-design AM tube tuner is a TRF design of some
sort, not a superheterodyne. The major issue appears to be how to get
the multiple stages (three stages appear necessary to attain
appropriate sensitivity and selectivity) all in "synch" (term used
loosely) for a given radio frequency.

Of course, thinking outside the box as I am wont of doing, I first of
all notice that the AM tuner will be used for commercial broadcasts
which are on strictly assigned frequencies: every 10khz in the U.S.
and every 9khz in Europe and elsewhere. If so, could we not dispense
with infinitely variable tuning and take a channel approach (like tv
receivers of old)? For TRF designs, this may be what is needed to
"perfectly synch" the three or more multiple stages, and do so in ways
not possible with the "1-D" restriction of a multiganged air tuning
capacitor (or variable inductor.) This may allow varying more
components for each channel to get the "perfect" fit between the
stages.

Anyway, I'll leave it to the experts to mull over the channel
approach to an AM tube tuner, to see if it will actually confer any
real advantages (especially for TRF circuits), and if so, how to
implement it in a practical sense (I have ideas), how to deal with
interference issues, etc.

Jon Noring

To get enough selectivity for local reception of AM stations,
and to get wide audio bandwidth, the Q of each LC circuit in a TRF needs to
be low.
But you still need at least 60 dB attenuation at 40 kHz away from the wanted
station.

I leave it up to the experts as to how one could have 10 kHz of AF bw
after 6 tuned circuits, even at the LF end of the band, where the Q at 550
kHz for just one LC circuit
would have to be as low as 27.5 to get 20 kHz of bandpass, -3 dB.

I don't think TRF would be a good idea.

Superhet operation with 2MHz IFTs would be far better.

Why don't you study the books to understand all the engineering involved
with the
status quo for tubed AM tuners?

Patrick Turner.

On Tue, 08 Jun 2004 16:11:02 GMT, "Frank Dresser"
wrote:


Getting wideband IF transformers will be a real problem. I don't know of
any NOS sources for them.

You can easily reduce the frequency selectivity of IF transformers by
adding resistors in parallel, though this will reduce sensitivity.

Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

On Tue, 08 Jun 2004 14:45:41 GMT, Jon Noring wrote:

On FM, especially among alternative FM stations, one often finds very
unusual musical programs being broadcast of music which the listener
does not have in their collection (it helps them to expand their
horizons and maybe go out and purchase said music on CD/vinyl.) In
addition, there are sometimes live broadcasts of concerts which will
never appear on CD/vinyl. (In Salt Lake City, the alternative FM
station I am thinking of is KRCL, http://www.krcl.org/ . Really a fun
station to listen to, especially the late Sunday night program
broadcasting 1920's to 1940's era recordings.)

It's very true that the level of audio postprocessing varies a great
deal around the world. In the UK all FM commercial broadcasters use
very high levels of compression (including Classic FM, a national
classical music station) because they like to sound 'loud'. Only the
BBC's classical station uses reasonable levels of compression and
limiting. This heavy compression is also used on digital feeds, where
it is completely unnecessary.

On AM there are certainly broadcasts which interest different people
for different reasons at different times. Live sports events not found
elsewhere, news, of course the venerable talk radio, and for some of
us, we like to spin the dial at night and see what distant stations we
can pull in.

Yes Jon, but that's not audiophile listening, it's using radio as it's
always been used for 80 years. You would do just as well to plug a
1970s Grundig Yacht Boy into your system (which is what I do :-) )

Well, maybe in the U.S. most stations cutoff at 3.5khz. Then that's
where they cutoff. However, the AM tuner design is intended for the
world, and as Patrick Turner noted, in Australia many broadcasters
have a much higher rolloff because of the "open highway" they have
on the BCB -- fewer stations spread farther apart.

Modern AM transmitters have a very sharp rolloff above a certain
frequency. Broadcasting above this would just waste transmitter power,
since (almost all) radios wouldn't be able to receive it because of
their IF selectivity characteristics. The 9kHz or 10kHz AM channel
width is just a convention, but once it has been adopted there's no
point in trying to receive a wider bandwidth - you'll just get
interference from adjacent stations.

There's nothing wrong with building your own high quality AM tuner,
either solid state or tube, but no matter how many gold lettered
Telefunken ECC83s you use it won't sound very good.

Agreed in principle. The AM tuner must deliver the highest possible
fidelity as broadcast, that's all. It must have very low distortion.

One question to ask is in various areas of the world (including the
U.S.) what is the distribution of HF cutoff among the many broadcast
stations? I doubt in the U.S. every broadcaster rolls off HF at
3.5khz, but maybe most do -- are there any AM stations in the U.S.
which have a much higher HF rolloff than 3.5khz? Note again Patrick's
comment on Australian AM broadcasters.

In the US and Canada, AM stations are allocated 10kHz bandwidth,
giving a theoretical 5kHz treble cutoff. In most other place that's
9kHz/4.5kHz. Stations transmit a more restricted frequency range than
this though, for a number of technical reasons. That's where my rough
and ready 3.5kHz figure came from.

Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

"Paul Sherwin"

In the US and Canada, AM stations are allocated 10kHz bandwidth,
giving a theoretical 5kHz treble cutoff. In most other place that's
9kHz/4.5kHz. Stations transmit a more restricted frequency range than
this though, for a number of technical reasons. That's where my rough
and ready 3.5kHz figure came from.

Best regards, Paul


** In Australia the AM channel spacing goes in 9 kHz increments, however
the transmitted bandwidth is not affected by that fact since the authorities
have kept a wide frequency separation between transmitters serving the same
areas.

The recovered audio from many transmitters is of good quality on speech
and music with high frequencies extending to 12 kHz in some cases - the
government owned networks being the best in this regard. At night, far
distant adjacent channel signals can produce an audible 9 kHz background
whistle which a sharp notch filter deals with most effectively. I use an
Australian made valve AM tuner designed for hi-fi reception of local
broadcasts and have tried out a few SS hi-fi AM designs as well.

The secret of good AM reception is the use of a balanced loop or frame
antenna to reduce man made and static noise to insignificance.



............ Phil

"Patrick Turner" a écrit dans le message

I don't expect anyone to pay 3c for what I say, which could be seen as OT.

You just met our village idiot it seems...

There is an unspoken rule here..._Ignore_ his posts. Let him talk to
himself.

We don't get into fight with village idiot like you do on RAT...Keeps rar+p
"clean"...;o)

Syl

"Jon Noring" wrote in message
...

Well, being the "OP", I want a high-audio performance, modern design
AM tuner to integrate into my audio system -- and I believe a lot of
tube-o-philes likewise want that -- but not everyone obviously. There
are several reasons why most higher-grade audio systems use separate
components, the reasons of which are obvious to most everyone. The AM
tuner is no different than other audio components in this regard.

[snip]

But AM is different than other media. AM is processed to somewhat
compensate for the deficiencies in typical radios and listening situations.
AM sounds compressed and on a wideband radio usually sounds over treble
boosted. A perfect AM tuner would reproduce this processing perfectly.

A decompressor circuit might be worth considering.

Frank Dresser

"Paul Sherwin" wrote in message
...

[snip]

Modern AM transmitters have a very sharp rolloff above a certain
frequency. Broadcasting above this would just waste transmitter power,
since (almost all) radios wouldn't be able to receive it because of
their IF selectivity characteristics. The 9kHz or 10kHz AM channel
width is just a convention, but once it has been adopted there's no
point in trying to receive a wider bandwidth - you'll just get
interference from adjacent stations.


If the received signal is very strong, the tuner's gain will have to be very
low. This will supress the adjacent channel interference quite well.



In the US and Canada, AM stations are allocated 10kHz bandwidth,
giving a theoretical 5kHz treble cutoff. In most other place that's
9kHz/4.5kHz. Stations transmit a more restricted frequency range than
this though, for a number of technical reasons. That's where my rough
and ready 3.5kHz figure came from.

Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

The FCC requires US AM radio stations to have an audio bandwidth between 4
and 10 kHz or a total bandwidth from 8 to 20 kHz. Typical radios with IF
transformers, rather than crystal or ceramic IF filters, don't have very
sharp skirt selectivity. Few radios will be able to block out a strong
adjecent channel 10 kHz off channel. Many can't block out a strong adjacent
20 kHz away. Some can't even block out a strong adjacent channel 30 kHz
away.

The FCC limits interference only partly by bandwidth restrictions. Mostly,
it uses geographic seperation and power restrictions.

By ear, I think most stations go to about 7 or 8 kHz audio. Many of the AM
stations are talkers, but the ads can really sparkle. There's one I hear
which sounds like it goes to the 10 kHz audio max.

Frank Dresser

Paul Sherwin wrote:

On Tue, 08 Jun 2004 16:11:02 GMT, "Frank Dresser"
wrote:

Getting wideband IF transformers will be a real problem. I don't know of
any NOS sources for them.

You can easily reduce the frequency selectivity of IF transformers by
adding resistors in parallel, though this will reduce sensitivity.

The typical impedance of an undamped 455 kHz undamped
IFT is between 20k and 50k at 455 kHz.
Adding some R to both coils reduces the load seen by the tube,
hence its gain drops because pentode IF amp tubes have a high Ra,
and gain varies with load.
So the gain of the IF amp drops maybe 6 dB with R loads to both LC circuits in
IFT2,
and gain drops the same amount in IFT1, powered by the F converter tube

The nose of the selectivity broadens, ie, the Q of the circuit reduces,
ie, the bandwidth passed by the IFT is broadened out,
but 50 kHz away from resonance the attenuation rolls off at 12 bD/octave.
The roll off of a typical single tuned LC IF circuit away from the pointy nose
shape of
the the curve is only 6 dB per octave. The profiles of typical response curves
for RF and IF
coils are illustrated plentifully in all the good old radio books.

So with damping R, and two IFTs, the amount of attenuation of signals only 50
kHz away from
the wanted station is reduced by at least 12 dB.
This may perhaps be enough to allow a station 50 Khz away to be heard in the
backgound of a wanted station,
especially if its one thats putting out 5,000 watts and the wanted station is
putting out only 300 watts,
and they are both within 10 miles of the receiver.

Therefore its important to have some selectivity, although quite broad,
ahead of the converter tube.
I use two low Q LC circuits in cascade which are slightly tuned apart
at the low end of the BCB so effectively broadening the RF bandwidth, but
enabling a steeper roll off away from the pass band.
At the top end of the BCB, the two input RF LC circuits are very nearly tuned
at the same F,
and since the Q is still low, but the Fo is higher, the pass band does not
cause
side band cutting and a reduction of RF bw which would then limit the audio
after another 4 tuned circuits in the IF stage.

To use TRF to do the same thing would be almost impossible, and
I would need at least 6 tuned circuits tuned in the same way, and a six gang
tuning cap,
along with a seventh gang to tune the oscillator. There would have to be two
low gain
IF amps, which could be cascoded triodes instead of pentodes.

Its a hell of a lot easier to do it all with a superhet.

Not many NOS IFTs.

The old ones seldon suffer from spending 50 years in an old radio set,
and they are actually fairly ruggedly made, with brass tuning shafts for the
ferrite cores,
and in cans which have kept out the pollution failrly well.

The coils are often pie wound coils of litz wire.
The distance between the coils determines the amount of magnetic coupling, and
most IFTs
have just the right distance to cause critical coupling which gives the flat
topped
bandpass characteristic so you get about 10kHz of BW from a typical 455 kHz
IFT.

This allows 5 kHz of audio.

Two IFTs of the same response will give 7 kHz of BW, which allows
3.5 kHz of audio BW.

Now the minute one cuts the single tube the IFT coils are mounted on and
moves them closer together, say by 5 mm, the magnetic coupling increases,
and the response usually widens, but not greatly, but the shape of the
response
becomes twin peaked either side of Fo.
If you have a twin peaked IF response it means the audio BW will be also
peaked up at say 4 kHz, before rolling off even more sharply than it did
before when the
response was flat.
But sometimes the first IFT1 is deliberately slightly overcoupled to give the
twin peaked response,
which then is compensated back to being flat by the following normally single
peaked response of
IF2.
But tuning could be strange, with a tuning indicator having to be set to the
slight
null between two peaks.
Alignment of the IFTs becomes more difficult.

This is why I suggest that an IF of 2 MHz be used instead of 455 kHz, because
for the same Q the pass band of say 3 normally critically coupled IFTs
would be nicely flat topped, but still have an overall wider bandpass than
two 455 kHz IFTs.
The would have to be two IF amps instead of 3, but their gain need only be
low,
so cacoded triodes come to mind.
The cascoded triode has an effectively very high
Ra looking into the anode of the top tube, and a 12AT7
would have Ra' = 1 Mohm. If RL was 20k, gain would be about 60.
12AU7 would also be OK with Ra' = 200k,
and gain about = 29 with cathodes fully bypassed.
But pentodes could be used, with 6BA6 as IFamp1, with AVC applied,
and 6AU6 as IF2, with no AVC applied to keep the final IF amplification
as linear as possible.
Distortion of the IF envelope shape will all be detected as audio distortion
to
the shape of the recovered audio at the diode detector stage.

It would be possible to perhaps simply remove turns from a 455 kHz
IF coil and halve the existing capacitors to raise the Fo to 2 Mhz.
This all has to be done carefully, so that after halving the cap size,
just the right no of turns are removed to get the IFT to tune to 2 MHz with
its tuning
slug in the middle of its travel range.
I have never done this, so perhaps its just easier to wind ones own
new IF coils, but large sized old ones with cans of 35mm dia are plentiful.
The tiny IFTs which became prevalent in radio sets in the 1960s are a PITA
to modify.

The use of 2MHz IFTs requires strict adherence to using shortest leads
from tubes to IFT connections, because the higher the F, the greater the
likelyhood
of oscillation and IF amp instability.
So the IFT and tube line up will be in a neat straight line, with small 7 pin
tubes being able
to be close as possible to the IFT cans, and perhaps with additional grounded
sheet metal shields up off the tube sockets.

Patrick Turner.












Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

Syl's Old Radioz wrote:

"Patrick Turner" a écrit dans le message

I don't expect anyone to pay 3c for what I say, which could be seen as OT.

You just met our village idiot it seems...

There is an unspoken rule here..._Ignore_ his posts. Let him talk to
himself.

We don't get into fight with village idiot like you do on RAT...Keeps rar+p
"clean"...;o)

Syl

Well, with all due respects to all gentlemen and possible idiots
on all groups to whom this subject thread is cross posted to,
I reserve the right to decide who I will ignore or not.

I will desperately try not step on anyone's toes as I act in well intentioned
freewill.

I won't budge from the idea that its possible to digitise the signal from the
antenna and simply apply
suitable algorithms, and get digital decoding, without all the phase shift
caused by consecutive tuned circuits.
Like on expensive CD players, a tubed output filter on the final DA converter
could be used,
and a decent sound could be had, at least in Oz, where the audio transmitted by
AM is often very
wide bandwidth, depite the fact that the networked stations send their radio
shows to air at different times,
and via satellite, before finally being broadcast by a local AM transmitter.
God knows how many links the signal goes through, afaik.

I have tried to address the problems caused by tuned circuit delays in
recommending
that 2 MHz IFTs be used.
I do think tubes are good for IF amps, certainly the last IF amp, because
of the huge dynamic range of the tubes, and far better performance
can be had compared to using j-fets and a lousy 12 volt B+ supply.
Some might argue silicon opamps would be better still.
I would have no objection to whatever they used, as long as it
achieves the goal of high quality sound, and it was a valid way of doing it, as
far as they were concerned.
But a j-fet balanced converter and first IF amp would be permissable
because the signals are so low before they get to a second and final IF amp.

To get ideal signal from an AM tubed receiver, the AF signal
from a 100% modulated AM IF carrier should be around 2vrms
at least, so the tube isn't working beyond its linear class A range.

Anyone have anything to say about this?

Patrick Turner.

Frank Dresser wrote:

"Jon Noring" wrote in message
...

Well, being the "OP", I want a high-audio performance, modern design
AM tuner to integrate into my audio system -- and I believe a lot of
tube-o-philes likewise want that -- but not everyone obviously. There
are several reasons why most higher-grade audio systems use separate
components, the reasons of which are obvious to most everyone. The AM
tuner is no different than other audio components in this regard.

[snip]

But AM is different than other media. AM is processed to somewhat
compensate for the deficiencies in typical radios and listening situations.
AM sounds compressed and on a wideband radio usually sounds over treble
boosted. A perfect AM tuner would reproduce this processing perfectly.

A decompressor circuit might be worth considering.

But how does one know how to apply an expander to exactly match
the inverse of the compressor characteristic?
I doubt two wrongs will make a right.

Anyhow, in Oz there isn't to much evidence of compression or emphasis of
audio HF on the stations worth listening to; I find the better the receiver,
the more like FM reception the AM signal becomes.

Patrick Turner.



Frank Dresser

Frank Dresser wrote:

"Paul Sherwin" wrote in message
...

[snip]

Modern AM transmitters have a very sharp rolloff above a certain
frequency. Broadcasting above this would just waste transmitter power,
since (almost all) radios wouldn't be able to receive it because of
their IF selectivity characteristics. The 9kHz or 10kHz AM channel
width is just a convention, but once it has been adopted there's no
point in trying to receive a wider bandwidth - you'll just get
interference from adjacent stations.

If the received signal is very strong, the tuner's gain will have to be very
low. This will supress the adjacent channel interference quite well.


In the US and Canada, AM stations are allocated 10kHz bandwidth,
giving a theoretical 5kHz treble cutoff. In most other place that's
9kHz/4.5kHz. Stations transmit a more restricted frequency range than
this though, for a number of technical reasons. That's where my rough
and ready 3.5kHz figure came from.

RDH4 says most AM BCB radio makers tried for a final IF bandwidth response of
3.5 kHz
That was in 1955/
Since then, the BW has shrunk in many sets to even less than 2 kHz, especially
in solid
state gear, giving horrid state AM listening.
No good turning up the treble control knob, there is no treble there to boost.


Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk

The FCC requires US AM radio stations to have an audio bandwidth between 4
and 10 kHz or a total bandwidth from 8 to 20 kHz. Typical radios with IF
transformers, rather than crystal or ceramic IF filters, don't have very
sharp skirt selectivity. Few radios will be able to block out a strong
adjecent channel 10 kHz off channel. Many can't block out a strong adjacent
20 kHz away. Some can't even block out a strong adjacent channel 30 kHz
away.

Oz local stations are rarely closer than 45 kHz, which is 5 x 9 kHz spaces.

In Canberra, we used to have 2XX community station of 300 watts on 1,008 kHz,
with 2CA of 5 Kw at 1,053 kHz, and it was a good test of any AM radio if
2CA couldn't be heard when tuned to 2XX.
My own radio allows me to pick up a weak signal at 27 kHz away from 2CA
without 2CA being heard.

Most simple transistor based tuners fail this test.
They have high Q single tuned IF coils.

7AD on 1008 kHz sometimes drifted in late at night all the way from Tasmania,
if conditions were freaky. Antenna type and location/direction minimised this
effect.



The FCC limits interference only partly by bandwidth restrictions. Mostly,
it uses geographic seperation and power restrictions.

By ear, I think most stations go to about 7 or 8 kHz audio. Many of the AM
stations are talkers, but the ads can really sparkle. There's one I hear
which sounds like it goes to the 10 kHz audio max.

Much AM is talkback from mobile telephones, and its pretty dreadful....



Patrick Turner.

"Patrick Turner" wrote in message
...




But how does one know how to apply an expander to exactly match
the inverse of the compressor characteristic?
I doubt two wrongs will make a right.

I had a book which described a very simple expander which was just a light
bulb in parallel with the speaker, if I recall. Loud passages would heat
the filament (probably not to incandesence) reduce the load of the bulb and
increase the volume even more. Quiet passages would let the bulb cool, load
the circuit and reduce the volume. It sounds goofy to me, and it's a
circuit which wasn't popular.

There were probably more sophicated expander circuits back then.

A modern sophicated decompressor circuit could match the curve of the
compressor, just as the dolby system does.




Anyhow, in Oz there isn't to much evidence of compression or emphasis of
audio HF on the stations worth listening to; I find the better the
receiver,
the more like FM reception the AM signal becomes.

Patrick Turner.


Here's some of what's been happening in radio audio processing over the
years in the US:

http://www.bext.com/histproc.htm

Frank Dresser

In article ,
Jon Noring wrote:
Well, being the "OP", I want a high-audio performance, modern design
AM tuner to integrate into my audio system -- and I believe a lot of
tube-o-philes likewise want that -- but not everyone obviously. There
are several reasons why most higher-grade audio systems use separate
components, the reasons of which are obvious to most everyone. The AM
tuner is no different than other audio components in this regard.

Maybe what you want is the old JW Miller passive AM tuner. No
active devices at all, just a bunch of tuned circuits and a detector
diode.

Mark Zenier Washington State resident

In article ,
"Frank Dresser" wrote:

"Patrick Turner" wrote in message
...




But how does one know how to apply an expander to exactly match
the inverse of the compressor characteristic?
I doubt two wrongs will make a right.

I had a book which described a very simple expander which was just a light
bulb in parallel with the speaker, if I recall. Loud passages would heat
the filament (probably not to incandesence) reduce the load of the bulb and
increase the volume even more. Quiet passages would let the bulb cool, load
the circuit and reduce the volume. It sounds goofy to me, and it's a
circuit which wasn't popular.

There were probably more sophicated expander circuits back then.

A modern sophicated decompressor circuit could match the curve of the
compressor, just as the dolby system does.


I am surprised at the size of this thread and how it has taken off, but
many of the comments seem to be either misleading as a result of wrong
facts or limited understanding of the technology involved. I have several
comments that I will lump together.

1. It has been variously stated that the audio bandwidth of AM
broadcasting is either 3.5 kHz, 5 kHz, or 10 kHz. In the US AM broadcast
channels are 20 kHz wide, so audio is effectively limited to a maximum of
10 kHz by law/regulation. It is my impression that most AM stations
transmit audio out to this legal maximum. Of course as HD-radio takes
hold this will change with the analog signal cutting off somewhere around
5 kHz. I know there are at least 2 active broadcast engineers that read
this group, perhaps they could fill us in on what the stations they are
involved with are actually doing as far as audio bandwidth goes?

2. The idea expressed above that a "modern sophicated decompressor
circuit could match the curve of the compressor" seems far fetched to me.
In the days of yore when audio processing consisted of a single broad band
compressor, and a broad band "peak limiter" one might have contemplated
this, at least as far as the compression part went, but today's audio
processing is much more complex. Processing today involves broad band
AGC, multiband compressors, plus multiband and broadband clippers in place
of the old "peak limiter". It isn't clear to me that this would be easy
to undo, or even possible. I don't know if the multiband aspect creates
problems for reversing the process or not, but how do you undo clipping,
and if there are any feed forward compressors involved it is possible that
the output isn't even a single valued function of the input, making
recovery mathematically impossible.

3. TRF receivers have been mentioned, and everyone seems to assume that a
TRF receiver would consist of cascaded single tuned resonators with RF
amplifier stages between. There is no reason why double tuned circuits,
similar to those used in the IF transformers of a superhetrodyne can't be
used in a TRF receiver, with all the selectivity/bandwidth benefits that
brings to the party. For examples see the Western Electric No. 10A
receiver, the J.W. Miller TRF receiver, the early Altec AM receiver, as
well as others.

4. It has been stated that constructing the various RF and IF coils,
especially IF transformers with variable bandwidth, that are required, is
one reason why people aren't doing this type of project. I would suggest
that a variable bandwidth double tuned IF filter can be built using
standard two terminal inductors, by using low side capacitive coupling. I
have a British Acoustical AM tuner that uses this approach in place of the
first IF transformer to provide variable bandwidth. Rather than using an
IF transformer with a tertiary winding to provide variable bandwidth, two
separate coils are used which are coupled by low side capacitive coupling,
where the amount of coupling can be switched to change the bandwidth just
the same as with the tertiary approach.

5. The thinking here seems to be limited to single tuned circuits for TRF
receivers, and double tuned IF transformers for superhetrodyne receivers.
There is no reason why one can't build more complex filters that will
provide better performance than an equivalent number of poles in ordinary
double tuned IFTs. Quad tuned filters are relatively easy to do, and it
is possible to go to even more poles in a single filter module, providing
an improved selectivity vs. bandwidth trade off.

6. It has been suggested that adding resistors across an ordinary IF
transformer will widen the audio bandwidth. This is not always true as
the Heath company illustrated in the manual for their BC-1A High Fidelity
AM tuner. They suggested adding a resistor to the first IFT to narrow the
bandwidth if interference from adjacent stations was encountered, and IIRC
they provide audio response graphs with and without the added resistor
showing how the resistor narrows the bandwidth. Actually I think that in
this case it is only the nose bandwidth that gets narrower, the bandwidth
further out beyond the audio range does increase as you would expect. I
think this effect is probably due to the fact that the first IFT in the
Heath, and other quality tuners, is overcoupled, and adding the resistor
eliminates the overcoupling effect narrowing the nose bandwidth. It pays
to be careful and make sure you know the theory and what you are doing, as
things don't always work as you might expect.

7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to see why
this should be true. Within reason, for bandwidths typical of audio
receivers, you should be able to build a filter at 455 kHz that has
effectively the same response as a 2 MHz filter. There is no need to
throw out the 455 kHz IF just to get wide bandwidth.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

Jon Noring schrieb:


In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

Have a look into the "Collins" S-series. These are state-of-the-art
tube sets 'til now. At least it's not the tubes alone but the fabulous
mechanical IF-filters giving outstanding results for a tube set.
Manuals with layout diagrams should be available on the web....

John Byrns wrote:

3. TRF receivers have been mentioned, and everyone seems to assume
that a TRF receiver would consist of cascaded single tuned
resonators with RF amplifier stages between. There is no reason why
double tuned circuits, similar to those used in the IF transformers
of a superhetrodyne can't be used in a TRF receiver, with all the
selectivity/bandwidth benefits that brings to the party. For
examples see the Western Electric No. 10A receiver, the J.W. Miller
TRF receiver, the early Altec AM receiver, as well as others.

I did a cursory check on the Internet, but did not yet find any
schematics for the mentioned receivers. Are they online somewhere?
Anyone?

I also found the following article from John posted back in 2000,
where he talks about the double tuned TRFs, such as WE-10A, J.W.
Miller, Collins (which I assume is the same one Volker Tonn
mentioned today), Meissner, and the Weeden (the last of which John
noted to be the best designed of all of them):

http://groups.google.com/groups?selm...&output=gplain

Unfortunately the URLs to the TRF schematics at John's site are not
working.

John, how exactly do these double tuned circuits work in TRF circuits
compared to using single tuned resonators, as depicted on slide 7 of:

http://www.technology.niagarac.on.ca...531unit6rx.ppt

John, I also recall you mentioning a while back about "modernizing"
one of these TRF receivers. What is the current state of your research
on these circuit designs? Have you advanced to the point that a
detailed schematic is right around the corner?

Thanks for posting your thoughts.

Jon Noring

Patrick Turner wrote:

I won't budge from the idea that its possible to digitise the signal
from the antenna and simply apply suitable algorithms, and get
digital decoding, without all the phase shift caused by consecutive
tuned circuits.

And I agree with Patrick. Despite my desire to have a nice, kit-made,
high-performance AM tube tuner, ultimately I think the best radio
tuner for sound quality and overall performance (whether AM, ASM, FM,
digital broadcast, etc.) is the pure digital system as described by
Patrick.

But do the necessary low-level A-D converters already exist? Is anyone
actually building radios on this principle, or are we still a few
years off?

Jon Noring

[p.s., pure Class D digital amps are continuing to improve, with
better switching and so on, so ultimately the only analog streams
we'll be dealing with will be radio signals captured by the antenna
(which will promptly be digitized), and the output to the speakers
from the last-stage PWM of the digital amplifier. Everything inbetween
will totally be digital, using advanced and inexpensive DSP to do
things not possible in the analog processing realm. The only realm
left for the audiophiles to play in will be speakers.)

Jon Noring wrote:

Patrick Turner wrote:

I won't budge from the idea that its possible to digitise the signal
from the antenna and simply apply suitable algorithms, and get
digital decoding, without all the phase shift caused by consecutive
tuned circuits.

And I agree with Patrick. Despite my desire to have a nice, kit-made,
high-performance AM tube tuner, ultimately I think the best radio
tuner for sound quality and overall performance (whether AM, ASM, FM,
digital broadcast, etc.) is the pure digital system as described by
Patrick.

But do the necessary low-level A-D converters already exist? Is anyone
actually building radios on this principle, or are we still a few
years off?

Jon Noring

There are virtual radios which can be installed in a PC.
Been around for years.
They involve a suitable antenna interface and sound card, and program on a
disc,
and were advertised for sale on the back of Electronics, the british
magazine.
The front plate of a radio communications receiver appears on the screen
and I guess you tune and select receiver functions by dabbing items on the
screen with a mouse.

[p.s., pure Class D digital amps are continuing to improve, with
better switching and so on, so ultimately the only analog streams
we'll be dealing with will be radio signals captured by the antenna
(which will promptly be digitized), and the output to the speakers
from the last-stage PWM of the digital amplifier. Everything inbetween
will totally be digital, using advanced and inexpensive DSP to do
things not possible in the analog processing realm. The only realm
left for the audiophiles to play in will be speakers.)

I think the world of totally digital is still some way off.

And while things like good vinyl replay still beats all digital disc
formats,
there will always be a following for analog.

I will be dead in 25 years, or deaf by then, so I won't give a hoot what
the human race does after that.

Patrick Turner.

Volker Tonn wrote:

Jon Noring schrieb:

In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

Have a look into the "Collins" S-series. These are state-of-the-art
tube sets 'til now. At least it's not the tubes alone but the fabulous
mechanical IF-filters giving outstanding results for a tube set.
Manuals with layout diagrams should be available on the web....

The mechanical filters are only good for reducing the BW of an existing IF
strip to make the receiver extremenly selective,
so a much reduced bandwidth is possible which isn't capable of wide AF BW.
Crystal filters are also used for the same purpose.


Since Mr Noring says he has regularly trawled the Net for everyone else's
expertise
on AM reception, but got nowhere, because he's still doin it,
why doesn't he gird his loins and put his shoulder to the task of learning
all about AM and radio engineering as spelled out so clearly in all the old
text books, and then
damn well build his own perfect AM radio???

Patrick Turner.

John Byrns wrote:

In article ,
"Frank Dresser" wrote:

"Patrick Turner" wrote in message
...




But how does one know how to apply an expander to exactly match
the inverse of the compressor characteristic?
I doubt two wrongs will make a right.

I had a book which described a very simple expander which was just a light
bulb in parallel with the speaker, if I recall. Loud passages would heat
the filament (probably not to incandesence) reduce the load of the bulb and
increase the volume even more. Quiet passages would let the bulb cool, load
the circuit and reduce the volume. It sounds goofy to me, and it's a
circuit which wasn't popular.

There were probably more sophicated expander circuits back then.

A modern sophicated decompressor circuit could match the curve of the
compressor, just as the dolby system does.

I am surprised at the size of this thread and how it has taken off, but
many of the comments seem to be either misleading as a result of wrong
facts or limited understanding of the technology involved. I have several
comments that I will lump together.

1. It has been variously stated that the audio bandwidth of AM
broadcasting is either 3.5 kHz, 5 kHz, or 10 kHz. In the US AM broadcast
channels are 20 kHz wide, so audio is effectively limited to a maximum of
10 kHz by law/regulation. It is my impression that most AM stations
transmit audio out to this legal maximum. Of course as HD-radio takes
hold this will change with the analog signal cutting off somewhere around
5 kHz. I know there are at least 2 active broadcast engineers that read
this group, perhaps they could fill us in on what the stations they are
involved with are actually doing as far as audio bandwidth goes?

The Oz situation is different to the US, as I and PA have indicated.

If two stations are 10 kHz apart on carrier F, and the both use
10 kHz modulation, then the sidebands of one station
will interfere and be heard when tuned to the other, if the signal strengths are
the same.
10 kHz notch filters won't stop the monkey chatter.




2. The idea expressed above that a "modern sophicated decompressor
circuit could match the curve of the compressor" seems far fetched to me.
In the days of yore when audio processing consisted of a single broad band
compressor, and a broad band "peak limiter" one might have contemplated
this, at least as far as the compression part went, but today's audio
processing is much more complex. Processing today involves broad band
AGC, multiband compressors, plus multiband and broadband clippers in place
of the old "peak limiter". It isn't clear to me that this would be easy
to undo, or even possible.

And two wrongs don't make a right.

I don't know if the multiband aspect creates
problems for reversing the process or not, but how do you undo clipping,
and if there are any feed forward compressors involved it is possible that
the output isn't even a single valued function of the input, making
recovery mathematically impossible.

Limiting stuffs audio, and it cannot be undone.



3. TRF receivers have been mentioned, and everyone seems to assume that a
TRF receiver would consist of cascaded single tuned resonators with RF
amplifier stages between. There is no reason why double tuned circuits,
similar to those used in the IF transformers of a superhetrodyne can't be
used in a TRF receiver, with all the selectivity/bandwidth benefits that
brings to the party. For examples see the Western Electric No. 10A
receiver, the J.W. Miller TRF receiver, the early Altec AM receiver, as
well as others.

With variable tuning? its hard to get right.

fixed IF tuning is far easier.



4. It has been stated that constructing the various RF and IF coils,
especially IF transformers with variable bandwidth, that are required, is
one reason why people aren't doing this type of project. I would suggest
that a variable bandwidth double tuned IF filter can be built using
standard two terminal inductors, by using low side capacitive coupling. I
have a British Acoustical AM tuner that uses this approach in place of the
first IF transformer to provide variable bandwidth. Rather than using an
IF transformer with a tertiary winding to provide variable bandwidth, two
separate coils are used which are coupled by low side capacitive coupling,
where the amount of coupling can be switched to change the bandwidth just
the same as with the tertiary approach.

Very hard to get right. I tried all that.
I tried tertiaries, but mechanical variation of the distance between IF coils
seemed to work best.



5. The thinking here seems to be limited to single tuned circuits for TRF
receivers, and double tuned IF transformers for superhetrodyne receivers.
There is no reason why one can't build more complex filters that will
provide better performance than an equivalent number of poles in ordinary
double tuned IFTs. Quad tuned filters are relatively easy to do, and it
is possible to go to even more poles in a single filter module, providing
an improved selectivity vs. bandwidth trade off.

6. It has been suggested that adding resistors across an ordinary IF
transformer will widen the audio bandwidth. This is not always true as
the Heath company illustrated in the manual for their BC-1A High Fidelity
AM tuner.

If it lowers the Q, the BW is widened, but at the expense of
attenuation just outside the band.
Its a bandaid measure.

They suggested adding a resistor to the first IFT to narrow the
bandwidth if interference from adjacent stations was encountered, and IIRC
they provide audio response graphs with and without the added resistor
showing how the resistor narrows the bandwidth.

??

Actually I think that in
this case it is only the nose bandwidth that gets narrower, the bandwidth
further out beyond the audio range does increase as you would expect. I
think this effect is probably due to the fact that the first IFT in the
Heath, and other quality tuners, is overcoupled, and adding the resistor
eliminates the overcoupling effect narrowing the nose bandwidth.

So its the rabbit eared response curve which is damped by the R,
thus narrowing the BW.

It pays
to be careful and make sure you know the theory and what you are doing, as
things don't always work as you might expect.

You got it.



7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to see why
this should be true.

Because for the same Q value, the pass band would be 4 times wider

Within reason, for bandwidths typical of audio
receivers, you should be able to build a filter at 455 kHz that has
effectively the same response as a 2 MHz filter. There is no need to
throw out the 455 kHz IF just to get wide bandwidth.

Its difficult to make a 455kHz typical old IFT produce a nice flat topped
20 kHz wide BW. Its either pointy nosed, undecoupled, or flat topped, critical
coupled,
or over critical or rabbit eared.
I have tried all that.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/