Hello, I'm restoring a Hallicrafters S-20R. I've managed to bring it
back from the grave by installing new caps, a few new resistors and
replacing a bad tube. Although its back to life, it still has some
issues, one I hope someone here can help with. When I touch the cap of
the 6K8 tube with my finger, the audio becomes much louder. Or the
sensitivity increases. Not sure which. But my question is why? What
should I look for in order to have the radio play at the volume without
holding my finger there. It gets very boring. Any help would be
appreciated.

Rod wrote:
Hello, I'm restoring a Hallicrafters S-20R. I've managed to bring it
back from the grave by installing new caps, a few new resistors and
replacing a bad tube. Although its back to life, it still has some
issues, one I hope someone here can help with. When I touch the cap of
the 6K8 tube with my finger, the audio becomes much louder. Or the
sensitivity increases. Not sure which. But my question is why? What
should I look for in order to have the radio play at the volume without
holding my finger there. It gets very boring. Any help would be
appreciated.


Alignment...or if this is happening only on BCB it may be a combination
of alignment and inferior antenna.

GL,
Bill

- exray - wrote:


Alignment...or if this is happening only on BCB it may be a combination
of alignment and inferior antenna.

GL,
Bill

I guess I should have also mentioned the possibility of bad rf coils
since thats not all that uncommon. You'll find out during alignment if
there's any bad ones.

GL

Many of these old receivers have been zapped by a lightning charge from
a nearby strike...It`s not at all uncommom to find an open RF coil in
the front end of the receiver..Usually this occurs on the band that the
rec is set on.Like BC band...If all bands show this condition it could
be a switch problem,or something else in RF section...GL W4PQW

You're adding a capacitor between ground and part of the tube when you
put your finger there. If the front end were tuned properly, this would
be detuning it. But it seems like it's improving the tuning, which makes
me think the tuning is way out. Look for open coils (easy to check with
a continuity tester), and bad ceramic capacitors in that stage.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

You have a missing slug in one or more of the RF coils.

--
Regards,
Gary...
"Scott Dorsey" wrote in message
...

You're adding a capacitor between ground and part of the tube when you
put your finger there. If the front end were tuned properly, this would
be detuning it. But it seems like it's improving the tuning, which makes
me think the tuning is way out. Look for open coils (easy to check with
a continuity tester), and bad ceramic capacitors in that stage.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Tue, 25 Apr 2006, Rod wrote:

Hello, I'm restoring a Hallicrafters S-20R. I've managed to bring it
back from the grave by installing new caps, a few new resistors and
replacing a bad tube. Although its back to life, it still has some
issues, one I hope someone here can help with. When I touch the cap of
the 6K8 tube with my finger, the audio becomes much louder. Or the
sensitivity increases.

I don't recognize what the 6K8 is. Audio first stage (diode-triode)? or
Mixer? A fair number of some of these tubes have, as the cap, the
connection to the control grid. If its an audio tube, then you should be
introducing more 60 cycle hum than anything else. When you say "the audio
becomes much louder" are you talking about the audio on the signal you are
listening to or background static or hum or what. I'm not at all familiar
with Hallicrafters before about S-38, S-40 vintage. Give us all some more
clues, and tube listing. I've read all the other responses up to the
moment of writing this posting; most are worth checking out.

If the cap is the control grid of the mixer, then just maybe you are
injecting--by capacitance pickup with your body (as antenna)--more
broadcast RF into the circuit than is coming in normally through whatever
else the input RF goes into (RF amplifier, coils, caps, whatever). In my
experience, lots of times you can touch the antenna terminal of a receiver
and pick up a lot of signal that would not be there if that terminal were
not connected to anything.

Not sure which. But my question is why? What
should I look for in order to have the radio play at the volume without
holding my finger there. It gets very boring. Any help would be
appreciated.

The 6K8 is the converter oscillator. When I put my finger on the top
to the tube, which has a cap that runs to the tuning mechanism, the
received signal becomes louder. It seems to happen on all bands. The
lower ends of each band are affected the most. I do have about a ten
foot wire connected to the antenna terminal. I also have another S-20R
which functions normally with respect to the received signal.
I hope this is the info you're asking for. Your help very much
appreciated.


Straydog wrote:
On Tue, 25 Apr 2006, Rod wrote:

Hello, I'm restoring a Hallicrafters S-20R. I've managed to bring it
back from the grave by installing new caps, a few new resistors and
replacing a bad tube. Although its back to life, it still has some
issues, one I hope someone here can help with. When I touch the cap of
the 6K8 tube with my finger, the audio becomes much louder. Or the
sensitivity increases.

I don't recognize what the 6K8 is. Audio first stage (diode-triode)? or
Mixer? A fair number of some of these tubes have, as the cap, the
connection to the control grid. If its an audio tube, then you should be
introducing more 60 cycle hum than anything else. When you say "the audio
becomes much louder" are you talking about the audio on the signal you are
listening to or background static or hum or what. I'm not at all familiar
with Hallicrafters before about S-38, S-40 vintage. Give us all some more
clues, and tube listing. I've read all the other responses up to the
moment of writing this posting; most are worth checking out.

If the cap is the control grid of the mixer, then just maybe you are
injecting--by capacitance pickup with your body (as antenna)--more
broadcast RF into the circuit than is coming in normally through whatever
else the input RF goes into (RF amplifier, coils, caps, whatever). In my
experience, lots of times you can touch the antenna terminal of a receiver
and pick up a lot of signal that would not be there if that terminal were
not connected to anything.

Not sure which. But my question is why? What
should I look for in order to have the radio play at the volume without
holding my finger there. It gets very boring. Any help would be
appreciated.

(quoted material below)

I read a couple other guy's comments as well. If there is an RF amplifier
ahead of the converter (converter = mixer+ oscillator), then something is
dead in that stage (coils, variable cap shorted/shorting, dead tube, open
interstage capacitor, and other possibilities). Dead tubes can have blown
filaments (if the receiver is on for a while, an open filament tube will
still be cold compared to the other tubes), or internal short, or gassy
tube, or weak cathode emission, lots of things. Whatever the RF stage is,
if that tube is identical to the IF stages, then swap the tube (RF into IF
socket) and if the whole receiver goes dead, then its that tube that is
dead. Get a new tube. Preferably you should try to locate someone with a
tube tester (this may not be practical in an age where everything is: i)
throw away, and ii) all solid state). All the other things you need to do,
need lots of checking and a schematic. If you can't get one, then you have
to trace it out by hand and use a tube manual to get pinouts on the tubes.
I'll keep reading from time to time; will post if I have any bright ideas.

===== no change to below, included for reference and context =====

On Wed, 26 Apr 2006, Rod wrote:

The 6K8 is the converter oscillator. When I put my finger on the top
to the tube, which has a cap that runs to the tuning mechanism, the
received signal becomes louder. It seems to happen on all bands. The
lower ends of each band are affected the most. I do have about a ten
foot wire connected to the antenna terminal. I also have another S-20R
which functions normally with respect to the received signal.
I hope this is the info you're asking for. Your help very much
appreciated.


Straydog wrote:
On Tue, 25 Apr 2006, Rod wrote:

Hello, I'm restoring a Hallicrafters S-20R. I've managed to bring it
back from the grave by installing new caps, a few new resistors and
replacing a bad tube. Although its back to life, it still has some
issues, one I hope someone here can help with. When I touch the cap of
the 6K8 tube with my finger, the audio becomes much louder. Or the
sensitivity increases.

I don't recognize what the 6K8 is. Audio first stage (diode-triode)? or
Mixer? A fair number of some of these tubes have, as the cap, the
connection to the control grid. If its an audio tube, then you should be
introducing more 60 cycle hum than anything else. When you say "the audio
becomes much louder" are you talking about the audio on the signal you are
listening to or background static or hum or what. I'm not at all familiar
with Hallicrafters before about S-38, S-40 vintage. Give us all some more
clues, and tube listing. I've read all the other responses up to the
moment of writing this posting; most are worth checking out.

If the cap is the control grid of the mixer, then just maybe you are
injecting--by capacitance pickup with your body (as antenna)--more
broadcast RF into the circuit than is coming in normally through whatever
else the input RF goes into (RF amplifier, coils, caps, whatever). In my
experience, lots of times you can touch the antenna terminal of a receiver
and pick up a lot of signal that would not be there if that terminal were
not connected to anything.

Not sure which. But my question is why? What
should I look for in order to have the radio play at the volume without
holding my finger there. It gets very boring. Any help would be
appreciated.

In article ,
Straydog wrote:


On Tue, 25 Apr 2006, Rod wrote:

Hello, I'm restoring a Hallicrafters S-20R. I've managed to bring it
back from the grave by installing new caps, a few new resistors and
replacing a bad tube. Although its back to life, it still has some
issues, one I hope someone here can help with. When I touch the cap of
the 6K8 tube with my finger, the audio becomes much louder. Or the
sensitivity increases.

I don't recognize what the 6K8 is. Audio first stage (diode-triode)? or
Mixer? A fair number of some of these tubes have, as the cap, the
connection to the control grid. If its an audio tube, then you should be
introducing more 60 cycle hum than anything else. When you say "the audio
becomes much louder" are you talking about the audio on the signal you are
listening to or background static or hum or what. I'm not at all familiar
with Hallicrafters before about S-38, S-40 vintage. Give us all some more
clues, and tube listing. I've read all the other responses up to the
moment of writing this posting; most are worth checking out.

If the cap is the control grid of the mixer, then just maybe you are
injecting--by capacitance pickup with your body (as antenna)--more
broadcast RF into the circuit than is coming in normally through whatever
else the input RF goes into (RF amplifier, coils, caps, whatever).

It is, indeed, the common grid connection for the triode-hexode mixer,
and I would agree that it could be RF pickup that's giving him the
extra audio output. Definitely points the finger at the RF stages
being out of alignment or otherwise faulty.

In my
experience, lots of times you can touch the antenna terminal of a receiver
and pick up a lot of signal that would not be there if that terminal were
not connected to anything.

Time for a signal generator, I suspect, and to check backwards from the
6K8 to the aerial terminal. If he's getting audio out then the IF,
detector, and audio stages are probably OK....

....oh, and check the RF stage tuning capacitor for bent/shorted plates.

Chris.

--

... ... File not found, I'll load something *I* think is interesting.