Hello All,
Here's another strange problem. R9 smokes when trying to power up the radio. I don't want to destroy the 35Z5 I have. I've checked everything but cannot find anything wrong. I replaced all the paper and filter capacitors. All the resistors are exactly the vaue they're supposed to be. There is no connection between B++ or B+ and the chassis. I'll check the resistoance from either of those to B-. Just a second. B++ 146 ohms B+ 3K ohms. This is between them and B-. Is the 126 ohms too low? I'll keep checking.

Thanks,

Dave

Hello again,
I see I made a typo.
Somehow I was thinking 146 but my fingers typed 126. The correct number is 146.

Sorry about that.

Dave
:Hello All,
: Here's another strange problem. R9 smokes when trying to power up the radio. I don't want to destroy the 35Z5 I have. I've checked everything but cannot find anything wrong. I replaced all the paper and filter capacitors. All the resistors are exactly the vaue they're supposed to be. There is no connection between B++ or B+ and the chassis. I'll check the resistoance from either of those to B-. Just a second. B++ 146 ohms B+ 3K ohms. This is between them and B-. Is the 126 ohms too low? I'll keep checking.
:
:Thanks,
:
:Dave

Hello All a 3rd time,
The service data clearly states and shows a 50B5 for this radio. But I noticed that pin 5 was unused. There was never any solder on it. Pin 5 should be the output pin. Then I see that the speaker transformer is connected to pin 7. If a 50B5 is put in that socket, pins 1 and 7 will be connected together, effectively making the short circuit that made R9 burn.
When I received this radio, someone had put a 35W4 in where the amplifier tube goes. There was no tube chart. Our service data for this model says 50B5. Maybe there should be a note, or there is a note that some models contain a 50C5. If this should happen to someone again, maybe they'll find this tip and check to see if the solder tab for pin 5 is unused on the amplifier tube socket.

I hope that this helped.

Thanks,

Dave

:Hello again,
: I see I made a typo.
:Somehow I was thinking 146 but my fingers typed 126. The correct number is 146.
:
:Sorry about that.
:
:Dave
::Hello All,
:: Here's another strange problem. R9 smokes when trying to power up the radio. I don't want to destroy the 35Z5 I have. I've checked everything but cannot find anything wrong. I replaced all the paper and filter capacitors. All the resistors are exactly the vaue they're supposed to be. There is no connection between B++ or B+ and the chassis. I'll check the resistoance from either of those to B-. Just a second. B++ 146 ohms B+ 3K ohms. This is between them and B-. Is the 126 ohms too low? I'll keep checking.
::
::Thanks,
::
::Dave

Dave

50C5 is correct. Pin #5 is plate on a 50B5 and has to be connected.

50B5 was replaced by 50C5 in radios due to UL requirements. This change has caused far more problems that it helped. As you found out the wrong tube ends up shorting B+.

Norm

:Hello All a 3rd time,
: The service data clearly states and shows a 50B5 for this radio. But I noticed that pin 5 was unused. There was never any solder on it. Pin 5 should be the output pin. Then I see that the speaker transformer is connected to pin 7. If a 50B5 is put in that socket, pins 1 and 7 will be connected together, effectively making the short circuit that made R9 burn.
: When I received this radio, someone had put a 35W4 in where the amplifier tube goes. There was no tube chart. Our service data for this model says 50B5. Maybe there should be a note, or there is a note that some models contain a 50C5. If this should happen to someone again, maybe they'll find this tip and check to see if the solder tab for pin 5 is unused on the amplifier tube socket.
:
:I hope that this helped.
:
:Thanks,
:
:Dave
:
::Hello again,
:: I see I made a typo.
::Somehow I was thinking 146 but my fingers typed 126. The correct number is 146.
::
::Sorry about that.
::
::Dave
:::Hello All,
::: Here's another strange problem. R9 smokes when trying to power up the radio. I don't want to destroy the 35Z5 I have. I've checked everything but cannot find anything wrong. I replaced all the paper and filter capacitors. All the resistors are exactly the vaue they're supposed to be. There is no connection between B++ or B+ and the chassis. I'll check the resistoance from either of those to B-. Just a second. B++ 146 ohms B+ 3K ohms. This is between them and B-. Is the 126 ohms too low? I'll keep checking.
:::
:::Thanks,
:::
:::Dave

:Dave
:
: 50C5 is correct. Pin #5 is plate on a 50B5 and has to be connected.
:
: 50B5 was replaced by 50C5 in radios due to UL requirements. This change has caused far more problems that it helped. As you found out the wrong tube ends up shorting B+.

Norm:
Tell me more about this, why should UL care what kind of output tube an AA=5 (or in this case an AA-4) had?
TNX
Lewis

Lewis,
I hadn't thought of this but that may be why R9 is there instead of just a jumper. That's so there isn't a total short circuit. The resistor will burn and discolor. In this radio's case it also took out the B+ portion of the 35Z5. The 35Z5 is another great invention. It acts as a fuse. The filament will open if there's a problem, and the emission will permanently drop to almost zero if there's a B+ problem. They may cost more than a fuse but they work great.
The UL is concerned with safety. If the radio didn't pass UL inspection, I don't think it was allowed to be sold. Or maybe nobody would buy it without the UL seal. I'm not sure how it works. It was probably proven to the UL that if the 50B5 was used instead of a 50C5, some wafts of smoke appear, with R9 installed, and then nothing. There's no fire hazard after the resistor opens. The radio wont work at all that way but it's safer, maybe, than if the jumper was there.

Dave

::Dave
::
:: 50C5 is correct. Pin #5 is plate on a 50B5 and has to be connected.
::
:: 50B5 was replaced by 50C5 in radios due to UL requirements. This change has caused far more problems that it helped. As you found out the wrong tube ends up shorting B+.
:
:
:Norm:
:Tell me more about this, why should UL care what kind of output tube an AA=5 (or in this case an AA-4) had?
:TNX
:Lewis