11-16-2015, 10:37 PM
Not to hijack your thread. But I have a 39-30, and I'm just sort of curious if yours has the same factory changes as mine did.
I've seen at least 2 other threads describing this change (picture below). Basically it seems Philco took AVC off the IF grid. They disconnected the secondary of the 2nd IF from the AVC line, and instead tied it in to the CT bias voltage resistor via a 490k resistor and they added a .05uF bypass cap. If you look at the schematic for the 39-36 (which is almost the exact same circuit/chassis, but shoved into a console), the schematic documents this circuit from the factory.
The other 2 changes are in the tone circuit. I've seen one other post about R25 (hanging off the tone tap). It's listed as 32k. But in the radio it was 51k from the factory, as was mine.
And the other change is also in the tone circuit, but I haven't seen anyone mention. C39 on the tone control is listed as .006 uF, but was .008 uF from the factory. Although, that is probably such a small difference, it doesn't matter much. Edit: Actually, I now see this was the cap that someone put a bumble bee in on yours.
As for my 39-30, I'm chasing down a distortion issue. There is a thread over at ARF that some people have been helping me with, but no luck so far. I had a thread here too earlier in the year, but never got much traction. I'd love to compare some notes with you when you finish yours up to see if I can find any discrepancies on mine.
I've seen at least 2 other threads describing this change (picture below). Basically it seems Philco took AVC off the IF grid. They disconnected the secondary of the 2nd IF from the AVC line, and instead tied it in to the CT bias voltage resistor via a 490k resistor and they added a .05uF bypass cap. If you look at the schematic for the 39-36 (which is almost the exact same circuit/chassis, but shoved into a console), the schematic documents this circuit from the factory.
The other 2 changes are in the tone circuit. I've seen one other post about R25 (hanging off the tone tap). It's listed as 32k. But in the radio it was 51k from the factory, as was mine.
And the other change is also in the tone circuit, but I haven't seen anyone mention. C39 on the tone control is listed as .006 uF, but was .008 uF from the factory. Although, that is probably such a small difference, it doesn't matter much. Edit: Actually, I now see this was the cap that someone put a bumble bee in on yours.
As for my 39-30, I'm chasing down a distortion issue. There is a thread over at ARF that some people have been helping me with, but no luck so far. I had a thread here too earlier in the year, but never got much traction. I'd love to compare some notes with you when you finish yours up to see if I can find any discrepancies on mine.
