Hello,

I have a 2A that I was unable to get the passband tuner setup so that
the pitch of the noise was equal on both sides of the center.

I setup a sweep generator, 0.1v pk-pk, sweeping from 40 - 60 KHz, in
on pin 5 of V4. I setup an oscilloscope on pin 1 of V5. A marker
output on the sweep generator is used as a trigger.

Doing this, I can clearly see a narrow passband that is shifted around
by the twist of the knob. On the 4.8 KHz position, the passband is
greatly widened, as expected.

Now, back to the narrow mode. There is ALOT of ripple on that
passband, and the sides are not symetrical. One side had a slow
rolloff, while the other had a far faster one. That explains the
greater amount of high frequency hissing in one sideband.

I opened the tuner. Four slugs are ganged together and mounted on a
spring machanism. Each slug is mounted on a coiled wire, which is
soldered to the part that moves them all together. Unlike the 2B and
2C, the slugs are not adjustable. I really want the set to work
correctly, so here is what I'm thinking of doing:

Take out the passband tuner, mount it to a wooden board. Take the
front cover off of the tuner, and install a simple nut/bracket to
simulate the action of the tuning knob. Unsolder and free the slugs.
Using the same sweeping mechanism, adjust the slugs for 2.4 KHz, 6dB
voltage, and as flat on the top as possible. Solder back into place,
reinstall into the radio.

BUT! I remember basic troubleshooting. Failures have a cause. WHY did
the passband tuner to out of tune? Caps in the circuit failed? A short
somewhere? I'll find out, but I am wondering if my method here makes
sense.

Comments?

--
David Goncalves
W1EUJ

"Dave Goncalves" wrote in message
...
Hello,

I have a 2A that I was unable to get the passband tuner
setup so that
the pitch of the noise was equal on both sides of the
center.

I setup a sweep generator, 0.1v pk-pk, sweeping from 40 -
60 KHz, in
on pin 5 of V4. I setup an oscilloscope on pin 1 of V5. A
marker
output on the sweep generator is used as a trigger.

Doing this, I can clearly see a narrow passband that is
shifted around
by the twist of the knob. On the 4.8 KHz position, the
passband is
greatly widened, as expected.

Now, back to the narrow mode. There is ALOT of ripple on
that
passband, and the sides are not symetrical. One side had a
slow
rolloff, while the other had a far faster one. That
explains the
greater amount of high frequency hissing in one sideband.

I opened the tuner. Four slugs are ganged together and
mounted on a
spring machanism. Each slug is mounted on a coiled wire,
which is
soldered to the part that moves them all together. Unlike
the 2B and
2C, the slugs are not adjustable. I really want the set to
work
correctly, so here is what I'm thinking of doing:

Take out the passband tuner, mount it to a wooden board.
Take the
front cover off of the tuner, and install a simple
nut/bracket to
simulate the action of the tuning knob. Unsolder and free
the slugs.
Using the same sweeping mechanism, adjust the slugs for
2.4 KHz, 6dB
voltage, and as flat on the top as possible. Solder back
into place,
reinstall into the radio.

BUT! I remember basic troubleshooting. Failures have a
cause. WHY did
the passband tuner to out of tune? Caps in the circuit
failed? A short
somewhere? I'll find out, but I am wondering if my method
here makes
sense.

Comments?

--
David Goncalves
W1EUJ

My R4-B is similar. Following the instructions gets it
usable but certainly not symmetrical. I have not yet gotten
at this in depth partly because I don't have a sweep
oscillator and I think one is probably necessary to tune
this thing properly.
If you don't know the history of your RX (meaning bought
it new) its quite possible someone else tried tuning it.
Also, perhaps there was a little mechanical drift in the
permeability tuned coils. I wish there was more service
information available for Drake stuff. I am about to
undertake fixing what I _think_ is a problem in the balanced
modulator of a T-4XB, acts like there may be a bad diode.
There is a Drake mailing list. I joined it but after getting
a confirming message there has been no traffic whatever.


--

--
Richard Knoppow
Los Angeles
WB6KBL

"Richard Knoppow" wrote in message
m...


My R4-B is similar. Following the instructions gets it usable but
certainly not symmetrical. I have not yet gotten at this in depth partly
because I don't have a sweep oscillator and I think one is probably
necessary to tune this thing properly.
If you don't know the history of your RX (meaning bought it new) its
quite possible someone else tried tuning it. Also, perhaps there was a
little mechanical drift in the permeability tuned coils. I wish there was
more service information available for Drake stuff. I am about to
undertake fixing what I _think_ is a problem in the balanced modulator of
a T-4XB, acts like there may be a bad diode. There is a Drake mailing
list. I joined it but after getting a confirming message there has been no
traffic whatever.

Hi Richard,
Join the Drakeradio Yahoo group- active and a lot of knowledge.
You may be able to use Spectrogram 16 to characterize your filter. Disable
the AGC, no antenna, adjust the AF Gain for a usable trace, and run
Spectrogram 16 in the peak hold mode- after several minutes, you'll have a
nice plot of the filter characteristics.

Dale W4OP

"Dave Goncalves" wrote in message
...
I have a 2A that I was unable to get the passband tuner setup so
that the pitch of the noise was equal on both sides of the center.
I setup a sweep generator, 0.1v pk-pk, sweeping from 40 - 60 KHz,

[Technical details omitted for brevity]

BUT! I remember basic troubleshooting. Failures have a cause. WHY
did the passband tuner go out of tune? Caps in the circuit failed?
A short somewhere? I'll find out, but I am wondering if my method
here makes sense.

Dave,

You have my respect! Far too many hams do their troubleshooting of
vintage gear by first using a tube tester and then using a VTVM to
compare measured voltages to a chart. I have always recommended
that they first study the schematic until they understand the design
fully. Then they can use this knowledge to analyze the symptoms and
make an intelligent choice as to which circuits are causing those
symptoms. For example. if signals are weak on one band only, there
is little to be gained from working on the audio stages. Yes, your
methodology makes perfect sense.

While my first receiver was a Drake 2-B, this was nearly 45 years
ago, and I have no direct experience with the 2-A. But I think I
can offer a few suggestions.

I doubt if any of the capacitors failed in the sense that they did
not short or open. Moisture ingress over the years may have shifted
their values a little to the high side however. The coils in the 2-
B were wound on phenolic forms. Moisture ingress in these is very
likely, particularly if they are the traditional linen cambric
reinforced phenolic. Moisture will increase the shunt capacitance
seen by the coils and will lower their resonance frequency. Baking
the passband tuner assembly overnight at 140 degrees will remove
most of this moisture. Allow the assembly to cool for several hours
before testing it to allow it to return to room temperature.

I believe the coil slugs are powdered iron rather than ferrite.
These are more prone to wear and having small pieces break off the
ends since they are softer. Check carefully to see that the slugs
are intact. A little silicone grease can be applied to lubricate
them.

Before unsoldering the slugs, try adding 5 to 10 pF capacitors
across one coil at a time and note if the shape of the passband gets
worse or better. I would not bother with adding or removing
capacitance from the coupling capacitors yet. Getting a nice
symmetrical shape to the passband should come first. Then you can
adjust the center frequency like Drake suggests.

One final thought - using a sweep generator and an oscilloscope can
sometimes be misleading. The sweep rate should be low enough that
you do not see ringing. Also remember that the oscilloscope shows
voltage on a linear scale. If you have access to a spectrum
analyzer with a log scale, you can use a broadband noise generator
as the input signal. If you do this, you may have to average the
signal over many sweeps.

If you need to trim the coupling capacitors slightly, consider the
old approach of "gimmick" capacitors made from two pieces of
insulated wire twisted together. I would use PTFE (Teflon) or PVDF
(Kynar) insulated solid wire for longevity. PVDF is commonly used
for "wire-wrap" wire.

I think your approach is the best one and I am sure you will soon
have found the problem(s) and have that venerable old receiver in
use again.

--
73, Dr. Barry L. Ornitz WA4VZQ

[transpose digits to reply]

"Dale Parfitt" wrote in message
...

"Richard Knoppow" wrote in message
m...


My R4-B is similar. Following the instructions gets it usable but
certainly not symmetrical. I have not yet gotten at this in depth partly
because I don't have a sweep oscillator and I think one is probably
necessary to tune this thing properly.
If you don't know the history of your RX (meaning bought it new) its
quite possible someone else tried tuning it. Also, perhaps there was a
little mechanical drift in the permeability tuned coils. I wish there
was
more service information available for Drake stuff. I am about to
undertake fixing what I _think_ is a problem in the balanced modulator
of
a T-4XB, acts like there may be a bad diode. There is a Drake mailing
list. I joined it but after getting a confirming message there has been
no
traffic whatever.

Hi Richard,
Join the Drakeradio Yahoo group- active and a lot of knowledge.
You may be able to use Spectrogram 16 to characterize your filter. Disable
the AGC, no antenna, adjust the AF Gain for a usable trace, and run
Spectrogram 16 in the peak hold mode- after several minutes, you'll have a
nice plot of the filter characteristics.

Dale W4OP

Extremely minor variations can cause this. It is best to sweep the filter
then offset the tunable oscillators to bring things into line. Less than
100 Hz will have a great effect on the apparent noise between upper and
lower sideband. I would be more concerned with breaking the filter, since
you can't just replace it. The passband is variable.

Barry,

First, thanks for all the useful suggestions - I had set a slow 100 Hz
sweep, and applied a little averaging on the oscilloscope for the
response envelope. Alas, the spectrum analyser I have access to
bottoms out at 100 kHz, so the noise generator approach is no good for
me. That gimmick tip is ACE!!

I wouldn't personally discount the 'holistic' approach so generally. I
know that general component degradation has occurred with many of my
radios. As an example, most of the resistors in my HW-101 audio board
were outside of their tolerance. Electrolytics, we all know, have a
lifetime, and paper caps are known issues. Tubes do develop shorts and
some leakage. It's cheap and easy work to do - during which you find
the gross issues; with radios going past 50 years and several hands, I
have found it more likely that not that MORE than one issue will be
present. The complexity in the analysis goes up, sometimes 'by the
square' with each additional shortcoming. But you are right that one
has to eventually get down and perform an analysis of the operation of
a defective stage to come up with ways it could fail.

My method for a restoration is: *reading the manual*, visual
inspection, cleaning, switch/contact check and cleaning, tube check,
capacitor replacement (shotgun replacement of all paper and
electrolytic), resistor check, basic operating check, ALIGN if I've
changed anything in the RF circuits, then an full operations check.
I've found and repaired most of the latent issues by the time I get to
the last step, and I can have a fair amount of confidence in most
components being 'what they claim to be' when it does come time to
review the schematic for a particular issue.

David Goncalves
W1EUJ

You have my respect! Far too many hams do their troubleshooting of
vintage gear by first using a tube tester and then using a VTVM to
compare measured voltages to a chart. I have always recommended
that they first study the schematic until they understand the design
fully.

"Dale Parfitt" wrote in message
...

"Richard Knoppow" wrote in
message
m...


My R4-B is similar. Following the instructions gets it
usable but certainly not symmetrical. I have not yet
gotten at this in depth partly because I don't have a
sweep oscillator and I think one is probably necessary to
tune this thing properly.
If you don't know the history of your RX (meaning
bought it new) its quite possible someone else tried
tuning it. Also, perhaps there was a little mechanical
drift in the permeability tuned coils. I wish there was
more service information available for Drake stuff. I am
about to undertake fixing what I _think_ is a problem in
the balanced modulator of a T-4XB, acts like there may be
a bad diode. There is a Drake mailing list. I joined it
but after getting a confirming message there has been no
traffic whatever.

Hi Richard,
Join the Drakeradio Yahoo group- active and a lot of
knowledge.
You may be able to use Spectrogram 16 to characterize your
filter. Disable the AGC, no antenna, adjust the AF Gain
for a usable trace, and run Spectrogram 16 in the peak
hold mode- after several minutes, you'll have a nice plot
of the filter characteristics.

Dale W4OP
I am a member but your suggestion caused me to check the
web site. I found it was not set to send me e-mail. That's
why there seemed to be no activity. I re-set it. I also
checked other Yahoo groups I belong to and found another
that was not set right.
I downloaded the Spectrogram program and will try it.
However, I think a sweeper would be more useful for tuning.
I can do this the "old fashioned way" by plotting the
response curve, that's a bit of a PITA but it doesn't have
to be done often. That is on the back burner since the RX
works pretty well as it is and getting the TX working right
is of higher priority.


--

--
Richard Knoppow
Los Angeles
WB6KBL

"Dale Parfitt" wrote in message
...

"Richard Knoppow" wrote in
message
m...


My R4-B is similar. Following the instructions gets it
usable but certainly not symmetrical. I have not yet
gotten at this in depth partly because I don't have a
sweep oscillator and I think one is probably necessary to
tune this thing properly.
If you don't know the history of your RX (meaning
bought it new) its quite possible someone else tried
tuning it. Also, perhaps there was a little mechanical
drift in the permeability tuned coils. I wish there was
more service information available for Drake stuff. I am
about to undertake fixing what I _think_ is a problem in
the balanced modulator of a T-4XB, acts like there may be
a bad diode. There is a Drake mailing list. I joined it
but after getting a confirming message there has been no
traffic whatever.

Hi Richard,
Join the Drakeradio Yahoo group- active and a lot of
knowledge.
You may be able to use Spectrogram 16 to characterize your
filter. Disable the AGC, no antenna, adjust the AF Gain
for a usable trace, and run Spectrogram 16 in the peak
hold mode- after several minutes, you'll have a nice plot
of the filter characteristics.

Dale W4OP
I am a member but your suggestion caused me to check the
web site. I found it was not set to send me e-mail. That's
why there seemed to be no activity. I re-set it. I also
checked other Yahoo groups I belong to and found another
that was not set right.
I downloaded the Spectrogram program and will try it.
However, I think a sweeper would be more useful for tuning.
I can do this the "old fashioned way" by plotting the
response curve, that's a bit of a PITA but it doesn't have
to be done often. That is on the back burner since the RX
works pretty well as it is and getting the TX working right
is of higher priority.


--

--
Richard Knoppow
Los Angeles
WB6KBL