I recently replaced the caps in this radio that had been "mokeyed" with by a previous owner. I tested it thru a dim bulb tester and there were no shorts, but when I plugged it to straight a.c. everything seemed fine til the C12 electrolytic (20@25v)began to smoke. I think I have it wired correctly all tho the schematic is a little hard for me to follow. I have the positive between C9 and R9 and the negative to C8 and R12. There was no 15 ohm R3 in the radio that I can find but according to the schematic it should also be connected R12 and C8. Could this be the problem? I'm a novice and need any help or suggestions. Thanks, Allen

C12 polarity should be OK as you described it: C10, C11 and C12 were originally part of a triple cap unit with a common ground wire; the way that you described
having it wired was the same as it would have come from the factory.

Electrolytic caps will smoke if they are installed in reverse or their maximum DC working voltage is exceeded. With C12 removed, turn on the set and take a voltmeter measurement across its connection points in the set to see what voltage/polarity C12 was exposed to. If its more than 12 volts or so, you have found why it smoked.

Offhand, the only thing that I could see that might smoke C12 would be if C9 short-circuited. This would apply full B+ voltage across C12, which would surely cook it. Or, when you installed C12 you may have accidentally connected its + side to the wrong side (plate side) of C9 instead of to the audio output tube's cathode... that would have the same effect on C12 as a shorted C9.

After you get the cap sorted out, try to find R3. There's a good chance that it got vaporized by whatever destroyed the capacitor, since it is in the current path and is only 15 ohms.

:After you get the cap sorted out, try to find R3. There's a good chance that it got vaporized by whatever destroyed the capacitor, since it is in the current path and is only 15 ohms.
:
CV - Thanks so much. My confidence level has been boosted. I will look again at my connections, and reply back. Much appreciated. Allen

::After you get the cap sorted out, try to find R3. There's a good chance that it got vaporized by whatever destroyed the capacitor, since it is in the current path and is only 15 ohms.
::
:CV - Thanks so much. My confidence level has been boosted. I will look again at my connections, and reply back. Much appreciated. Allen

CV - I checked the voltage between the connection points of C12 with it removed and the radio out of the cabinet and not connected to the turntable or speaker and it was around 13 to 14 volts. I reconnected the C12 and it remained cool. However when I hooked up the radio to the speaker and the turntable motor the capacitor once again heated up and eventually popped.
I then checked the voltage between the connections and it was off the scale 200+. Where do you think I should look for the problem? What about either the speaker or TT motor would make the voltage jump? Please advise. Thanks, Allen

The turntable motor would have nothing to do with the problem. When you say "plug in the speaker" what hardware exactly are you plugging in? That is, is the output transformer physically mounted on the speaker, so that you are connecting the output transformer to the circuit when you plug in the speaker, or is just the transformer secondary circuit being connected to the speaker, with the primary remaining in the output tube plate circuit?

I am guessing that it is the former: the output transformer is mounted to the speaker, so with the "speaker unplugged" you will get no plate or screen voltage to the audio output tube. That's the only scenario relating to your symptom that would make sense.

Did you check that C9 is not shorted and that the positive side of C12 is going to the correct side of C9?

If you don't find anything conclusive with respect to a wiring error or a C9 short, I recommend that you snip C9 out of the circuit and replace C12 again. C9 may be breaking down under voltage. With C9 out of the circuit there is no reasonable way that high voltage can be getting onto the cathode of the output tube. C9 is for high frequency bypassing and the set will work without it (although it should be replaced after you find the problem).

It may make troubleshooting easier if you unbolt the speaker from the set and plug it into the radio while it is on the bench so that you can monitor voltages from turn-on. The phono motor is irrelevant so you can leave it disconnected.

:The turntable motor would have nothing to do with the problem. When you say "plug in the speaker" what hardware exactly are you plugging in? That is, is the output transformer physically mounted on the speaker, so that you are connecting the output transformer to the circuit when you plug in the speaker, or is just the transformer secondary circuit being connected to the speaker, with the primary remaining in the output tube plate circuit?
:
:I am guessing that it is the former: the output transformer is mounted to the speaker, so with the "speaker unplugged" you will get no plate or screen voltage to the audio output tube. That's the only scenario relating to your symptom that would make sense.
:
:Did you check that C9 is not shorted and that the positive side of C12 is going to the correct side of C9?
:
:If you don't find anything conclusive with respect to a wiring error or a C9 short, I recommend that you snip C9 out of the circuit and replace C12 again. C9 may be breaking down under voltage. With C9 out of the circuit there is no reasonable way that high voltage can be getting onto the cathode of the output tube. C9 is for high frequency bypassing and the set will work without it (although it should be replaced after you find the problem).
:
:It may make troubleshooting easier if you unbolt the speaker from the set and plug it into the radio while it is on the bench so that you can monitor voltages from turn-on. The phono motor is irrelevant so you can leave it disconnected.
:

:The turntable motor would have nothing to do with the problem. When you say "plug in the speaker" what hardware exactly are you plugging in? That is, is the output transformer physically mounted on the speaker, so that you are connecting the output transformer to the circuit when you plug in the speaker, or is just the transformer secondary circuit being connected to the speaker, with the primary remaining in the output tube plate circuit?
:
:I am guessing that it is the former: the output transformer is mounted to the speaker, so with the "speaker unplugged" you will get no plate or screen voltage to the audio output tube. That's the only scenario relating to your symptom that would make sense.
:
:Did you check that C9 is not shorted and that the positive side of C12 is going to the correct side of C9?
:
:If you don't find anything conclusive with respect to a wiring error or a C9 short, I recommend that you snip C9 out of the circuit and replace C12 again. C9 may be breaking down under voltage. With C9 out of the circuit there is no reasonable way that high voltage can be getting onto the cathode of the output tube. C9 is for high frequency bypassing and the set will work without it (although it should be replaced after you find the problem).
:
:It may make troubleshooting easier if you unbolt the speaker from the set and plug it into the radio while it is on the bench so that you can monitor voltages from turn-on. The phono motor is irrelevant so you can leave it disconnected.
:
CV - I already had the speaker out of the cabinet. The output transformer is mounted on the speaker with a 4 prong plug. That is what I plug onto the radio. The positive side of C12 is connected between R9 and C9.
I will check for a short on C9. I never found the 15 ohm R3. The high voltage comes in after I connect the speaker. Your help has been greatly educational, thanks. Allen

Looking at the schematic, it appears that if C8 were shorted, it could also smoke C12 by applying a high reverse DC voltage to it. So that would be another "likely suspect" if C9 is exonerated.

If either C8 or C9 shorted, R3 would be burned open, too.

:Looking at the schematic, it appears that if C8 were shorted, it could also smoke C12 by applying a high reverse DC voltage to it. So that would be another "likely suspect" if C9 is exonerated.
:
:If either C8 or C9 shorted, R3 would be burned open, too.
:
There is no R3. Does the speaker connection have anything to do with the problem? That is when the high voltage comes in. 13+ volts until the speaker is connected, then 200+. Neither C8 or C9 are shorted.

Did you physically remove both C9 and C8 from the radio and find that the high voltage is still present across C12? If you still have high voltage across C12 with both caps out of the circuit, there is one last thing to try: lift the wire from the output transformer to the 35L6 output tube at the tube socket (wrap the wire end with tape to insulate it, since it has B+ on it). Don't reinstall C8 and C9. Power up the set and measure across C12. If it is a dozen volts or so, I suspect that you have a shorted 35L6 tube. This is improbable but not impossible.

I agree that c-9 is a very likely suspect. Especially since those caps on the output see some very high spikes and can short... they are very often found leaky or shorted.

:I agree that c-9 is a very likely suspect. Especially since those caps on the output see some very high spikes and can short... they are very often found leaky or shorted.
:
I removed C8 and C9 and the voltage across the C12 connections still reads 290 volts. I have not lifted the wires coming from the transformer but unplugging the speaker drops the voltage eventually (but slowly) to around 14 volts, the same as with C8 and C9 in the circuit but without the speaker. Where to from here? Please direct further, any suggestions at all. Thanks, Allen

Does that 35L6 tube itself test good?

Maybe an internal short from cathode to plate or screen grid to cathode.
....if you do know that tube is good....

You should also carefully check the wiring on the 35L6 output tube socket.

Pull the 35L6 out and take some ohm readings looking for shorts between pins.

Maybe a solder blob.

You may have a short from the screen grid pin 4 to the cathode pin 8.

Maybe even a short between the plate pin 3 and the cathode pin 8.

That would be a good reason to explain why the Full B+ is on the cathode.

I agree- there are only so many ways that high voltage can get onto the cathode of the output tube:

(1) C9 is shorted
(2) C8 is shorted
(3) The output tube is internally shorted from the plate to the cathode (somewhat improbable)
(4) There is a miswire from a high voltage node in the set to the cathode of the output tube. This miswire could be an intentional mod (wire) or a solder splash or blob.
(5) The audio output transformer primary is shorted. If this is the case it would overcurrent the output tube and possibly lead to an internal tube short (plate or screen to cathode) due to heat distortion.

Did I miss anything? It should just be a matter of methodologically checking out each of the above possibilities. This isn't magic; there has to be a logical explanation for this fault.

I would proceed as follows, performing all four of the following actions:

(1) Look for "sneak paths" or a miswire from the audio output tube cathode to elsewhere in the radio.

(2) Replace C8 and C9 or just snip them out of the circuit temporarily- their short-term absence won't be a problem.

(3) Measure the resistance of the output transformer primary: if it is dead zero or a couple of ohms, the primary is shorted and it will quickly destroy the audio output tube. A good transformer should read a few hundred ohms (DC resistance).

(4) Have the audio output tube tested for shorts, or better yet, sub in a known-good (i.e., purchased tested from a tube broker) tube.

:I agree- there are only so many ways that high voltage can get onto the cathode of the output tube:
:
:(1) C9 is shorted
:(2) C8 is shorted
:(3) The output tube is internally shorted from the plate to the cathode (somewhat improbable)
:(4) There is a miswire from a high voltage node in the set to the cathode of the output tube. This miswire could be an intentional mod (wire) or a solder splash or blob.
:(5) The audio output transformer primary is shorted. If this is the case it would overcurrent the output tube and possibly lead to an internal tube short (plate or screen to cathode) due to heat distortion.
:
:Did I miss anything? It should just be a matter of methodologically checking out each of the above possibilities. This isn't magic; there has to be a logical explanation for this fault.
:
:I would proceed as follows, performing all four of the following actions:
:
:(1) Look for "sneak paths" or a miswire from the audio output tube cathode to elsewhere in the radio.
:
:(2) Replace C8 and C9 or just snip them out of the circuit temporarily- their short-term absence won't be a problem.
:
:(3) Measure the resistance of the output transformer primary: if it is dead zero or a couple of ohms, the primary is shorted and it will quickly destroy the audio output tube. A good transformer should read a few hundred ohms (DC resistance).
:
:(4) Have the audio output tube tested for shorts, or better yet, sub in a known-good (i.e., purchased tested from a tube broker) tube.
:
:Thanks guys, The 35L6 tests good on my tester. I have others I can try. I will follow all the suggestions and report back. I appreciate your patience! Allen

::I agree- there are only so many ways that high voltage can get onto the cathode of the output tube:
::
::(1) C9 is shorted
::(2) C8 is shorted
::(3) The output tube is internally shorted from the plate to the cathode (somewhat improbable)
::(4) There is a miswire from a high voltage node in the set to the cathode of the output tube. This miswire could be an intentional mod (wire) or a solder splash or blob.
::(5) The audio output transformer primary is shorted. If this is the case it would overcurrent the output tube and possibly lead to an internal tube short (plate or screen to cathode) due to heat distortion.
::
::Did I miss anything? It should just be a matter of methodologically checking out each of the above possibilities. This isn't magic; there has to be a logical explanation for this fault.
::
::I would proceed as follows, performing all four of the following actions:
::
::(1) Look for "sneak paths" or a miswire from the audio output tube cathode to elsewhere in the radio.
::
::(2) Replace C8 and C9 or just snip them out of the circuit temporarily- their short-term absence won't be a problem.
::
::(3) Measure the resistance of the output transformer primary: if it is dead zero or a couple of ohms, the primary is shorted and it will quickly destroy the audio output tube. A good transformer should read a few hundred ohms (DC resistance).
::
::(4) Have the audio output tube tested for shorts, or better yet, sub in a known-good (i.e., purchased tested from a tube broker) tube.
::
::Thanks guys, The 35L6 tests good on my tester. I have others I can try. I will follow all the suggestions and report back. I appreciate your patience! Allen
:
:
I believe you said R3 is missing, R3 is the path to B- for the cathode also thru R9. If this is missing when the tube conducts you will have B+ on the cathode with no path to B-. The capacitor is connected to ground so it will have full B+ across it.
What is the resistance from the cathode to B- (B- not chassis ground), It should be about 165 ohms, R9 + R3.

Hi Allen,
One note of caution. Beware of pulled 35L6GT. I had two in my box both tested good and a radio with a 35L6GT that tested good and sounded awful.
It sounded awful with the other two 35L6GTs, too.
Not until I got an NOS 35L6GT did I find the problem.

I had the same thing happen with type 42's.

All the Best,

Bill G.