Patrick Turner wrote:
I finally got the revised Stromberg Carlson radio tuner section running about as
well as it ever will.

It includes the dual cathode follower stage for which I posted a schematic at abse and
abpr last week.

The only changes I made was to use IN914 diodes, and 200pF and 1M for the audio RC
peak&hold
network, as well as use a 12AT7 for the CF parts.

The idle DV at the cathode of V1 is at +48 v without a carrier, but
with a test signal carrier a little larger than the strongest station here,
The DV at the C after D1 was +103v, indicating a carrier of
55 pk volts, and the audio at 400 Hz at 90% modulation was 36 vrms, or
51v pk.

I measured the thd with a 1 kHz low distortion af signal,
and got 3% at this level of signal, which is about 2 dB short of total
overload if the IF amp.
At 30% modulation, thd was about 0.2%.

Don't forget to do a measurement at 5KHz, as various distrotion
products can go up for higher audio frequencies at the demodulator.
Namely tangent distortion, which may not show at 1KHz but may show
at 5KHz.


Then when I reduced the RF input by 30 dB, the audio output and carrier level
all fell by 10 dB, due to AGC action, and remeasured and got the same thd figures.

The distortion is so low in the receiver including the detector that its thd
cannot be measured because it is dominated by the thd in the RF test gene,
which measures similarly when I measured it alone.

The RF gene can achieve about 96% mod but the thd becomes quite high at about 7%,
because the pentode RF tube used does not cut off at a linear rate, and
I really should have used a pair of PP tubes with a NFB loop to make the RF modulated
signal
have far less thd in the AF envelope shape.

So the conclusion is that the radio I have just got running
does not produce the buckets of thd like so many other radios I have tested,
and anyone is welcome to use the design I had in my posted schematic.

It was of some importance to get the AGC application correct.
Too much directly applied AGC will virtually cut off the IF vari mu pentode IF amp,
so that with 28vrms of audio from as big a carrier which will support that,
you may only have 0.5 mA of anode current, and when you plot
the load line, it just isn't quite right.

Modulation Rise it's called in RDH4. If you have an RF amp stage, use
a variable mu tube there (signals are still small) and change the IF
tube from say a 6BA6 to a 6AU6 or such sharp cutoff tube. Another
solution is to use only a fraction of the AVC voltage on the IF tube.
Voltage divider is the usual method.

Better to make sure that with extreme levels of carrier, the anode current is
over 1.5 mA, and thd I expect is a little lower.

For lower levels of carrier, tube current will increase to a max of 5 mA
at no carrier at all.
There should be some method of applying at least about -1.5 v to IF and mixer tube grids
because
such tubes go a bit beserko when biased close to 0V.

The local oscillator (usually a 6BE6) develops a fair amount of negative
bias that you could tap. Connect a 10 or so megohm resistor physically
near the oscillator (to lessen added stray capacitence) G1 and connect
the other end to the AVC line.

Another method is to add more resistance to the cathode resistor on the
IF tube and bypass it to ground. This will make the G1 look to have
more negative bias on it as seen by the cathode. And reduce the gain
some. Additional shielding and careful lead dress might help tame that
tube.

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

I have seen no reference of your interpretive methodology in any
text books, and the text book methods to which I adhere to explain
it all nicely, and I don't have any intention of going right through
all that long and tortuous discussion again.

And I wouldn't ask you to, if you notice I am not disputing your method,
I am simply disputing your apparent claim that my method is invalid. I
would ask you for one favor though, could you cite some of the textbooks
that explain your method so nicely?

I would have a dozen on my shelf which explain radio theory sufficiently
well, including RDH4, and 11 others.

Ahh, the old weapons of mass destruction excuse, you have the RDH4 and 11
other text books, and yet you can't come up with a citation for your
method?

I won't have the same books as you have, but apart from RDH4,
I have Terman's Radio Engineering,
about 6 different dated copies of ARRL,
The british Communications Handbook, 5th Ed,
Phillips Radio Paractice, Essentials of Radio by Sluurzberb&Osterfield,
Applied Electronics by the staff of the Dept of Massacgusets insitute of
Technology,

Electrical and Electronic Engineering by John D Ryder,

Of those I have at least the RDH4, and Terman's Radio Engineering, plus
possibly one or two more, how about some page numbers where I can find an
explanation of your definition of the rate of increase of the attenuation
of a tank circuit around resonance?

Most of the radio books I have do have explicit graphs and explanations of the
response
of RF and IFTs, with varying amounts of mutual coupling.
You don't need the page numbers from me, the info is in there.
The attenuation rates are shown on the graphs
And also there is a statement in RDH4 about sideband cutting, with a narrow bw RF /
IF response,
which underlines the importance of requiring a wide RF bw to get a wide audio
response.



and I am too lazy to copy out the titles of the other approximate 10 books
I have read on old fashioned electronics which all describe filters the same
way, but not the way you do.

Well I guess that about says it all, you are simply one of those old
fashioned blokes who can't change his ways to adopt newer and better
methods.

Well in a later post I did take the trouble to name my sources.

And I am not a lazy old bugger who never gets off his arse to find out by looking
into things.

I shouldn't have to do all this for you; your library should be embellished with
enough old books about radio to make all of what I am saying perfectly clear.



If you wanna uphold your methods, go write a book.

I suppose I could, but why, I am not a textbook author, and my methods are
not original with me, I am not nearly that clever. As I have said before
I took them straight out of the modern filter design textbooks, the books
on this subject have already been written by others, many times over, the
field is way too crowded. You need to expand your reading list beyond
those smelly old radio textbooks, the old blokes didn't know everything,
you might learn something new from some more up to date reading, if you
can even call it that.

The smelly old textbooks say it all so well that there isn't any need to
re-invent the wheel.
The application of the theory contained didn't lead to great BCB AM radios very
often because the
radio industry was infested with bean counters and charlatans.
This fact don't detract from the wisdom of the old books.

The technology of tube radios is ancient history which will never again be
the important techno mainstream thing it was, like steam engines.
But the old technology is still fascinating, and great sound can be had with the
right circuits.



All the books backing up what I am saying are on the shelves for you to read.

Page numbers please, if you can't cite page numbers it is nothing more
than BS! Don't worry, I'm not going to hold my breath waiting, or
anything like that.

You have to do your own study; I can't and I won't do it for you.

I was frustrated when I started to study the subject 10 years ago, and nobody could
answer
1,001 questions I had, so I simply went to second hand bookstores and snapped up
whatever was there,
which seems impossible now because the sharks and collectors seem to have emptied
the stores,
and then I read and copied reams at the university libraries.

But I also built and re-built a few radios.
Including AM/FM types.

Without having done anything in the workshop, I'd know SFA.

Patrick Turner.



Regards,

John Byrns

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

Robert Casey wrote:

Patrick Turner wrote:
I finally got the revised Stromberg Carlson radio tuner section running about as
well as it ever will.

It includes the dual cathode follower stage for which I posted a schematic at abse and
abpr last week.

The only changes I made was to use IN914 diodes, and 200pF and 1M for the audio RC
peak&hold
network, as well as use a 12AT7 for the CF parts.

The idle DV at the cathode of V1 is at +48 v without a carrier, but
with a test signal carrier a little larger than the strongest station here,
The DV at the C after D1 was +103v, indicating a carrier of
55 pk volts, and the audio at 400 Hz at 90% modulation was 36 vrms, or
51v pk.

I measured the thd with a 1 kHz low distortion af signal,
and got 3% at this level of signal, which is about 2 dB short of total
overload if the IF amp.
At 30% modulation, thd was about 0.2%.

Don't forget to do a measurement at 5KHz, as various distrotion
products can go up for higher audio frequencies at the demodulator.
Namely tangent distortion, which may not show at 1KHz but may show
at 5KHz.

At 35 vrms of undistorted output at 400 Hz, the detector seems fine, but at 2 khz the
tangential distortion starts.
But with 10vrms output of audio this distortion occurs first at a much higher F.
Reducing the value of the peak and hold cap from 200pF to 100 pF would improve the undistorted
bw.




Then when I reduced the RF input by 30 dB, the audio output and carrier level
all fell by 10 dB, due to AGC action, and remeasured and got the same thd figures.

The distortion is so low in the receiver including the detector that its thd
cannot be measured because it is dominated by the thd in the RF test gene,
which measures similarly when I measured it alone.

The RF gene can achieve about 96% mod but the thd becomes quite high at about 7%,
because the pentode RF tube used does not cut off at a linear rate, and
I really should have used a pair of PP tubes with a NFB loop to make the RF modulated
signal
have far less thd in the AF envelope shape.

So the conclusion is that the radio I have just got running
does not produce the buckets of thd like so many other radios I have tested,
and anyone is welcome to use the design I had in my posted schematic.

It was of some importance to get the AGC application correct.
Too much directly applied AGC will virtually cut off the IF vari mu pentode IF amp,
so that with 28vrms of audio from as big a carrier which will support that,
you may only have 0.5 mA of anode current, and when you plot
the load line, it just isn't quite right.

Modulation Rise it's called in RDH4. If you have an RF amp stage, use
a variable mu tube there (signals are still small) and change the IF
tube from say a 6BA6 to a 6AU6 or such sharp cutoff tube.

In this radio I wanted to have a vary U octal tube, and the 6G8 was chosen because I had it.
In another radio, I use a 6BX6, with fixed bias.

Another
solution is to use only a fraction of the AVC voltage on the IF tube.
Voltage divider is the usual method.

That is indeed what I am doing, but it takes awhile to get the divider values right.



Better to make sure that with extreme levels of carrier, the anode current is
over 1.5 mA, and thd I expect is a little lower.

For lower levels of carrier, tube current will increase to a max of 5 mA
at no carrier at all.
There should be some method of applying at least about -1.5 v to IF and mixer tube grids
because
such tubes go a bit beserko when biased close to 0V.

The local oscillator (usually a 6BE6) develops a fair amount of negative
bias that you could tap. Connect a 10 or so megohm resistor physically
near the oscillator (to lessen added stray capacitence) G1 and connect
the other end to the AVC line.

The ECC35 is a triode hexode, and the arrangements I have made for it are fine, and a bit
different to
6BE6, which I quite like.

Another method is to add more resistance to the cathode resistor on the
IF tube and bypass it to ground. This will make the G1 look to have
more negative bias on it as seen by the cathode. And reduce the gain
some. Additional shielding and careful lead dress might help tame that
tube.

In triode hexodes, the cathode should be grounded, lest the oscillator cathode current
be injected into the hexode cathode circuit; the grid of the triode oscillator
feeds into a grid of the hexode, and that's all that is wanted.

Patrick Turner.

Hi Patrick,

All your comments on text book references below are beside the point, what
I was asking for is a citation for a textbook that explains yours and
Phil's assertion that the rate of increase in the attenuation of a LC tank
circuit is greatest near the "nose", and decreases further from
resonance? Please note that I am not disputing yours and Phil's
viewpoint, I came to understand your perspective during the "Thick as a
Brick" thread back in January. You say this perspective is the one used
in old radio text books, but I have never seen it mentioned in an old
radio text book, hence I was hoping you could help me with a citation to a
text book that uses/explains your perspective? Just because I haven't
seen it doesn't mean it isn't there, since I never looked for it in the
past.

You seem to have forgotten that I changed the subject after you started
talking about the thickness of your skull, you acknowledged the change of
subject in a couple of posts, but now you have drifted back to an earlier
subject and assuming that is what I am asking for citations on.


Regards,

John Byrns


In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

I have seen no reference of your interpretive methodology in any
text books, and the text book methods to which I adhere to explain
it all nicely, and I don't have any intention of going right
through
all that long and tortuous discussion again.

And I wouldn't ask you to, if you notice I am not disputing
your method,
I am simply disputing your apparent claim that my method is
invalid. I
would ask you for one favor though, could you cite some of the
textbooks
that explain your method so nicely?

I would have a dozen on my shelf which explain radio theory
sufficiently
well, including RDH4, and 11 others.

Ahh, the old weapons of mass destruction excuse, you have the RDH4
and 11
other text books, and yet you can't come up with a citation for your
method?

I won't have the same books as you have, but apart from RDH4,
I have Terman's Radio Engineering,
about 6 different dated copies of ARRL,
The british Communications Handbook, 5th Ed,
Phillips Radio Paractice, Essentials of Radio by Sluurzberb&Osterfield,
Applied Electronics by the staff of the Dept of Massacgusets insitute of
Technology,

Electrical and Electronic Engineering by John D Ryder,

Of those I have at least the RDH4, and Terman's Radio Engineering, plus
possibly one or two more, how about some page numbers where I can find an
explanation of your definition of the rate of increase of the attenuation
of a tank circuit around resonance?

Most of the radio books I have do have explicit graphs and explanations of the
response
of RF and IFTs, with varying amounts of mutual coupling.
You don't need the page numbers from me, the info is in there.
The attenuation rates are shown on the graphs
And also there is a statement in RDH4 about sideband cutting, with a
narrow bw RF /
IF response,
which underlines the importance of requiring a wide RF bw to get a wide audio
response.



and I am too lazy to copy out the titles of the other approximate 10 books
I have read on old fashioned electronics which all describe filters
the same
way, but not the way you do.

Well I guess that about says it all, you are simply one of those old
fashioned blokes who can't change his ways to adopt newer and better
methods.

Well in a later post I did take the trouble to name my sources.

And I am not a lazy old bugger who never gets off his arse to find out
by looking
into things.

I shouldn't have to do all this for you; your library should be
embellished with
enough old books about radio to make all of what I am saying perfectly clear.



If you wanna uphold your methods, go write a book.

I suppose I could, but why, I am not a textbook author, and my methods are
not original with me, I am not nearly that clever. As I have said before
I took them straight out of the modern filter design textbooks, the books
on this subject have already been written by others, many times over, the
field is way too crowded. You need to expand your reading list beyond
those smelly old radio textbooks, the old blokes didn't know everything,
you might learn something new from some more up to date reading, if you
can even call it that.

The smelly old textbooks say it all so well that there isn't any need to
re-invent the wheel.
The application of the theory contained didn't lead to great BCB AM
radios very
often because the
radio industry was infested with bean counters and charlatans.
This fact don't detract from the wisdom of the old books.

The technology of tube radios is ancient history which will never again be
the important techno mainstream thing it was, like steam engines.
But the old technology is still fascinating, and great sound can be had
with the
right circuits.



All the books backing up what I am saying are on the shelves for you
to read.

Page numbers please, if you can't cite page numbers it is nothing more
than BS! Don't worry, I'm not going to hold my breath waiting, or
anything like that.

You have to do your own study; I can't and I won't do it for you.

I was frustrated when I started to study the subject 10 years ago, and
nobody could
answer
1,001 questions I had, so I simply went to second hand bookstores and
snapped up
whatever was there,
which seems impossible now because the sharks and collectors seem to
have emptied
the stores,
and then I read and copied reams at the university libraries.

But I also built and re-built a few radios.
Including AM/FM types.

Without having done anything in the workshop, I'd know SFA.

Patrick Turner.



Regards,

John Byrns

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


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

John Byrns wrote:

Hi Patrick,

All your comments on text book references below are beside the point, what
I was asking for is a citation for a textbook that explains yours and
Phil's assertion that the rate of increase in the attenuation of a LC tank
circuit is greatest near the "nose", and decreases further from
resonance? Please note that I am not disputing yours and Phil's
viewpoint, I came to understand your perspective during the "Thick as a
Brick" thread back in January. You say this perspective is the one used
in old radio text books, but I have never seen it mentioned in an old
radio text book, hence I was hoping you could help me with a citation to a
text book that uses/explains your perspective? Just because I haven't
seen it doesn't mean it isn't there, since I never looked for it in the
past.

You seem to have forgotten that I changed the subject after you started
talking about the thickness of your skull, you acknowledged the change of
subject in a couple of posts, but now you have drifted back to an earlier
subject and assuming that is what I am asking for citations on.

I don't have the time to debate this any longer.
I don't want to repeat what I have already said.

I suggest yet again you satisfy your curiosity to inform yourself of the wonderments

we see with LC tuned circuits by reading whatever books exist on the subjects,
and I am sure there is a pile of material on the web.

My methods and perceptions have led to successfully building or modifying AM radios
to
a far better level of performance than the status quo, and I have thus prooved at
least to myself
the effectiveness of my education, which I promoted to be able to use it, and not
merely to be a
"knowledgeable do-little".

Patrick Turner.



Regards,

John Byrns

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:

I have seen no reference of your interpretive methodology in any
text books, and the text book methods to which I adhere to explain
it all nicely, and I don't have any intention of going right
through
all that long and tortuous discussion again.

And I wouldn't ask you to, if you notice I am not disputing
your method,
I am simply disputing your apparent claim that my method is
invalid. I
would ask you for one favor though, could you cite some of the
textbooks
that explain your method so nicely?

I would have a dozen on my shelf which explain radio theory
sufficiently
well, including RDH4, and 11 others.

Ahh, the old weapons of mass destruction excuse, you have the RDH4
and 11
other text books, and yet you can't come up with a citation for your
method?

I won't have the same books as you have, but apart from RDH4,
I have Terman's Radio Engineering,
about 6 different dated copies of ARRL,
The british Communications Handbook, 5th Ed,
Phillips Radio Paractice, Essentials of Radio by Sluurzberb&Osterfield,
Applied Electronics by the staff of the Dept of Massacgusets insitute of
Technology,

Electrical and Electronic Engineering by John D Ryder,

Of those I have at least the RDH4, and Terman's Radio Engineering, plus
possibly one or two more, how about some page numbers where I can find an
explanation of your definition of the rate of increase of the attenuation
of a tank circuit around resonance?

Most of the radio books I have do have explicit graphs and explanations of the
response
of RF and IFTs, with varying amounts of mutual coupling.
You don't need the page numbers from me, the info is in there.
The attenuation rates are shown on the graphs
And also there is a statement in RDH4 about sideband cutting, with a
narrow bw RF /
IF response,
which underlines the importance of requiring a wide RF bw to get a wide audio
response.



and I am too lazy to copy out the titles of the other approximate 10 books
I have read on old fashioned electronics which all describe filters
the same
way, but not the way you do.

Well I guess that about says it all, you are simply one of those old
fashioned blokes who can't change his ways to adopt newer and better
methods.

Well in a later post I did take the trouble to name my sources.

And I am not a lazy old bugger who never gets off his arse to find out
by looking
into things.

I shouldn't have to do all this for you; your library should be
embellished with
enough old books about radio to make all of what I am saying perfectly clear.



If you wanna uphold your methods, go write a book.

I suppose I could, but why, I am not a textbook author, and my methods are
not original with me, I am not nearly that clever. As I have said before
I took them straight out of the modern filter design textbooks, the books
on this subject have already been written by others, many times over, the
field is way too crowded. You need to expand your reading list beyond
those smelly old radio textbooks, the old blokes didn't know everything,
you might learn something new from some more up to date reading, if you
can even call it that.

The smelly old textbooks say it all so well that there isn't any need to
re-invent the wheel.
The application of the theory contained didn't lead to great BCB AM
radios very
often because the
radio industry was infested with bean counters and charlatans.
This fact don't detract from the wisdom of the old books.

The technology of tube radios is ancient history which will never again be
the important techno mainstream thing it was, like steam engines.
But the old technology is still fascinating, and great sound can be had
with the
right circuits.



All the books backing up what I am saying are on the shelves for you
to read.

Page numbers please, if you can't cite page numbers it is nothing more
than BS! Don't worry, I'm not going to hold my breath waiting, or
anything like that.

You have to do your own study; I can't and I won't do it for you.

I was frustrated when I started to study the subject 10 years ago, and
nobody could
answer
1,001 questions I had, so I simply went to second hand bookstores and
snapped up
whatever was there,
which seems impossible now because the sharks and collectors seem to
have emptied
the stores,
and then I read and copied reams at the university libraries.

But I also built and re-built a few radios.
Including AM/FM types.

Without having done anything in the workshop, I'd know SFA.

Patrick Turner.



Regards,

John Byrns

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

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

In article , Patrick Turner
wrote:

I don't have the time to debate this any longer.

Hi Patrick,

You seem to be the one that wants a debate where one is not necessary, or
asked for. There is nothing to debate here, I understand yours and Phil's
position in a qualitative sense, but I find yours and Phil's approach
somewhat counter intuitive, just as you find my approach counter
intuitive. You say that your approach to LC tuned circuits is described
in many text books, I have not found any, although admittedly I have not
been searching specifically for information on your approach to LC tuned
circuits. All I have asked you for is a simple citation to a textbook
where I can find out more about your approach, especially the quantitative
aspects of your approach, and how to make use of it in design problems.
While it is easy to understand your idea from a qualitative perspective, I
don't understand how to actually apply it. I would prefer to learn that
from a textbook rather than taking your time to have you explain it
further.

I don't want to repeat what I have already said.

I'm not asking you to repeat anything, I am only asking you to provide a
citation for one of the textbooks that gives a good description of your
approach to LC tuned circuit design, you have not done that before. Your
continued unwillingness to provide a reference to one of the many
textbooks that you have said describe your perspective on LC tuned circuit
design, while continuing to make the claim, has made it pretty obvious
that your claims relative to textbook explanations is nothing but BS.
That is not to say that your observations are BS, I unraveled that back in
January, it is just the claim that your method may be found in textbooks
that smacks of BS.

I suggest yet again you satisfy your curiosity to inform yourself of the
wonderments we see with LC tuned circuits by reading whatever books exist
on the subjects, and I am sure there is a pile of material on the web.

Yes, I have several books on my bookshelf that explain the "wonderments we
see with LC tuned circuits", that is not a problem, but they explain
methods that are quite different from yours, I am simply looking for a
reference that will more fully explain your methods than what I have been
able to figure out on my own, especially from a quantitative perspective.

Sadly the answer to my question has become crystal clear.


Regards,

John Byrns


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

John Byrns wrote:

In article , Patrick Turner
wrote:

I don't have the time to debate this any longer.

Hi Patrick,

You seem to be the one that wants a debate where one is not necessary, or
asked for. There is nothing to debate here, I understand yours and Phil's
position in a qualitative sense, but I find yours and Phil's approach
somewhat counter intuitive, just as you find my approach counter
intuitive. You say that your approach to LC tuned circuits is described
in many text books, I have not found any, although admittedly I have not
been searching specifically for information on your approach to LC tuned
circuits. All I have asked you for is a simple citation to a textbook
where I can find out more about your approach, especially the quantitative
aspects of your approach, and how to make use of it in design problems.
While it is easy to understand your idea from a qualitative perspective, I
don't understand how to actually apply it. I would prefer to learn that
from a textbook rather than taking your time to have you explain it
further.

I don't want to repeat what I have already said.

I'm not asking you to repeat anything, I am only asking you to provide a
citation for one of the textbooks that gives a good description of your
approach to LC tuned circuit design, you have not done that before. Your
continued unwillingness to provide a reference to one of the many
textbooks that you have said describe your perspective on LC tuned circuit
design, while continuing to make the claim, has made it pretty obvious
that your claims relative to textbook explanations is nothing but BS.
That is not to say that your observations are BS, I unraveled that back in
January, it is just the claim that your method may be found in textbooks
that smacks of BS.

I suggest yet again you satisfy your curiosity to inform yourself of the
wonderments we see with LC tuned circuits by reading whatever books exist
on the subjects, and I am sure there is a pile of material on the web.

Yes, I have several books on my bookshelf that explain the "wonderments we
see with LC tuned circuits", that is not a problem, but they explain
methods that are quite different from yours, I am simply looking for a
reference that will more fully explain your methods than what I have been
able to figure out on my own, especially from a quantitative perspective.

Sadly the answer to my question has become crystal clear.

Regards,

John Byrns

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

I hope I don't bore you with long winded repetitions
of what is contained in RDH4 and all the other reputable text books.
But whatever they say, I agree with, so I am not needed for citations and page
numbers.
Go find out for yourself like I did, and be confident.

But to make an ideal AM tuner for local BCB to get at least 9 kHz of bw at low
thd and noise,
the most critical part of the exercize is to make the response of the IF
channel using two IFTs
to give around 8 kHz of bw of audio.

This means 16 kHz of IF bw.

To acheive that, its easier to utilise a pair of existing conventional
IFTs rather than wind one's own which necessitates the use of litz wire,
and special patterned widing techniques.

The IFTs chosen don't need to be a matched pair, but I prefer the types from
1950's radios with larger cans and simple solenoid windings with inductive
tuning.

A preliminary investigation should be made to ascertain the response
at 455 kHz by means of ideally placing the IFT as is into an existing IF amp,
with the detector with two CF as I have posted already established,
The input to the IF amp can be to the IFamp tube grid with about the normal
working bais level.
Only a small input signal is needed, to get about 20vrms of carrier signal at
the anode of the IFT tube
This can easily be measured using a simple peak reading volt meter using
a shielded low input capacitance probe, where you have a 500 pF cap
feeding an SS diode with its anode grounded, and the rectified peak +DV level
generated by the
simple detector is then divided by a 2.2M and 270k divider to approximately
give a 10 : 1 reduction of the DV level.
A schematic for such a simple detector is similar to the AGC diode detector in
the schemo I posted.
Many of the ARRL books carry such a simple RF detector schematic for
immediately
converting RF voltages into a DV which is so much more easily measured
remotely without losses or affecting signal level being measured in the high
impedance circuits concerned.
The peak DV can be read by a DVM across the 270k, and x 10 for the real value.
Its a primitive way to measure the anode RF level, but good enough for what we
want.
With such an RF voltage measurer, we can check the input and output levels of
the IFT,
to make sure the tube is not overloaded, and the insertion losses of the IFT
are not excessive.


The frequency adjustable test signal should be set at exactly 455 kHz, measured
with a ditital F meter,
and the carrier level adjusted for about 28 pk volts read from our network.
With the AGC voltage application shunted at the 0.05 uF first cap in the AGC
line

The IFT is tuned up to give the highest AGC voltage at the detector.

I have a modulated test carrier, so I use a low F of modulation of 100 Hz,
and 30% AM is sufficient.

A page is ruled up in an exercize book to record the response for 50 kHz each
side of 455 kHz,
with one line down the page representing -3 dB.
A CRO is used to monitor the level of recovered audio from the detector,
and perhaps you will have about 2vrms of audio to measure.

The 100 Hz sine wave is displayed on the CRO so it occupies the full height of
the screen.

Then you adjust the F of the sig gene and plot the -3,-6,-12,-18,-24 dB audio
levels and record the
carrier F at which these audio levels occur.
One does the graph for each side of the 455 kHz centre F.

The dots are joined, and the graph can be drawn of the IFT selectivity shape.

The 100 Hz audio will decline very nearly exactly with the decline in RF
response of the IFT,
because the 100 Hz modulation causes sideband frquencies only 100 Hz each side
of 455 kHz.

With an average garden variety IFT that an average radio maker of 1950 may have
made,
you will get -3 dB points at around 3 kHz each side of the 45 kHz, with steep
sides beyond this, then
some flattening out beyond the -12 dB points.
The -3 dB points are known as the F1 and F2 response poles, and F2 - F1 = the
bandwidth.
The overall response should look like a section through a bell,
and there should be an attenuation of -24 dB at about 50 kHz away from 455 kHz.

The aim is to make the IFT response wider, so the transformer is removed from
the chassis,
and the windings removed from the cans, and the tube on which the IF coils are
wound has a 5mm wide
peice of tube former cut out without wrecking the litz wire, cap leads, or
anything else.
Each of the 7 strands of fine wire in the litz wire must remain intact.

A plastic or carboard tube is found to tightly fit over the tube stubs of IF
coils, and the the coils moved closer together,
and reassembled into the can, and back onot the chassis.
The response measurement is repeated, and we should see a wider bandwidth
response,
but the slopes of the attenuation beyond the -3 dB will remain the same.
The reponse may even show a twin, but quite unevely peaked response, and that
because when the
IFTs are peaked up with coils closer the mistake was to tune the IFT so one
coil is centred on 455 kHz,
and the other centred on the side peak F which may be at 458 or 452 kHz, so a
if there are two peaks noticable when peaking up the IFT while aligning it, the
response peaks must be
symetrical each side of the 455 kHz, which might appear in the centre of a
trough
in the response.

Its all quite fiddly, and the novice will get trapped everytime.

The IF coil distance is repeatedly adjusted for a slightly troughed response
with two peaks,
and the bw should then be around 12 kHz.

Then we add some damping resistance of say 150 k to each of the LC windings.

This will usually reduce the sightly twin peaked reposne to a single one,
but which has a broad response of 10 kHz.

Sometimes 100 k dmaping R should be added, but the general idea is to
close the distance between IF coils, and use the least R dampers to produce the
widest
single peaked bandwidth with a nicely symetrical shape, which indicates each LC
is exactly
tuned to 455 kHz.

We repeast the whole process again with the second IFT.

The IFTs can then have their coils carefully glued so their distance cannot
vary, and finally
reassembled and mounted in the set with the mixer tube added.

With the RF input tuning gang tuned to the lowest possible RF frequency,
the IF gene signal can be reduced, and fed into the RF input, and enough 455
kHz will
get through to the mixer anode to test the IF response again,
only this time we can have the AGC allowed to be operational, lest we overload
the
mixer and IF amp with too much signal.

The IFs should be realigned for the highest AGC negative voltage, and
symetrical
response shape, which now should show the -3 dB points at say 7 kHz each side
of 455 kHz,
and at least twice the rates of attenuation recorded with one IFT.

The input test F should then be changed to an RF input signal of say 550 kHz,
and the set tuned to this F for maximum AGC, and quick check of the IF
frequency should reveal
455 kHz, if not, the set slightly tuned so that is the case.
The tuning gang should nearly be fully closed.
If not, the oscilator coil slug is adjusted to where 500 kHz should be.
The set should tune up to the high end of the band, so that RF of 1,650 kHz can
be tuned,
if not, the oscilator gang trim cap adjusted to allow 1,650 kHz.
With the set tuned to 550 kHz, the RF input coil slug should be adjusted for
max AGC,
which shows the RF LC is now tuned to the low RF while producing 455 kHz IF.
The set is then tuned to around 1,400 kHz, and the trim cap on the RF tuning
gang adjusted for
max AGC.
This indicates the RF input is tuned to the high RF whilst producing 455
kHz.IF.

With a constant level of RF input, the AGC level across tha band should vary
by not more than +/- 3 dB.
Sometimes its best to align the best tracking at 650 kHz and 1,300 kHz,
if the wanted stations are all in this bandwidth.

Notice how we have not simulated or calculated a single thing during
this whole tedious process, which should take the unititiated a couple of days
to get right,
using the right type of gear, and making only a few mistakes which are
discovered
along the way by those with a skeptical distrust of their abilities, and an
attitude that they
must proove beyond any doubt that everything they measure all adds up to the
design aim.

The same tedious methods for alignment exist in the text books I have
described.

Little attention in the text books has been given to achieving a pass band as
wide as
8 kHz at least, because the textbooks were often written for the mass market
makers
by manufacturers of tubes, who wanted to make it easy to use their products
with as much ease as possible.
The books give little account of using an audio step filter to slightly
emphasize the
recovered HF audio so that we can boost the initial audio roll off caused by
the
IF response so that the response is stretched a bit further from 7 kHz to 9
kHz.
Trying for more than this is high impossible because an RC compensation network

can only have a slight boost, before the roll off due to the IF shape causes a
massive
roll off rate which is impossible to compensate with any RC network.
And we don't want to over compensate, and end up with a hump in the audio
response
at say 2 kHz.

I am sure anything I left out can be found in the books, so don't bother being
lazy
and asking me questions they can answer.

Patrick Turner.

In article ,
Patrick Turner wrote:

I hope I don't bore you with long winded repetitions of what is
contained in RDH4 and all the other reputable text books. But
whatever they say, I agree with, so I am not needed for citations and
page numbers.

Why don't you print all your posts in a book. You certainly have written
enough of them.

So far in June - July you have cross posted 70 threads and hundreds of
messages to RRS.

Stop being a cross posting moron.

--
Telamon
Ventura, California

Telamon wrote:

In article ,
Patrick Turner wrote:

I hope I don't bore you with long winded repetitions of what is
contained in RDH4 and all the other reputable text books. But
whatever they say, I agree with, so I am not needed for citations and
page numbers.

Why don't you print all your posts in a book. You certainly have written
enough of them.

So far in June - July you have cross posted 70 threads and hundreds of
messages to RRS.

Stop being a cross posting moron.

I continue to write as much as I feel like to whoever I feel like.

You will always fail 100% to limit my rights to free speach.

Get your book reading skills up to scratch.

You don't know how to contribute to the discussion, so why not stay out of
it?

Patrick Turner.



--
Telamon
Ventura, California

Patrick Turner wrote:



Stop being a cross posting moron.


I continue to write as much as I feel like to whoever I feel like.

Its sad that your willingness to be an useful partner on Usenet is
overwhemelmed by this "I'll continue... TO BE A NET BLOWHARD" attitude.
Do it in 50 words or less and I'll send you a prize.

-BM