01-10-2019, 09:55 PM
I'm pretty well convinced that my radio is wired correctly. I've checked every single connection...every tube socket, every terminal strip, every function switch terminal. Everything checks out, so I'm hunting for a bad component. I've replaced every paper and electrolytic cap, and I've replaced nearly every resistor on the main chassis. Since the tuner sub-chassis is difficult to get I didn't previously check the resistors or mica caps on it. But now I have checked the resistors and found 3 to be way out of tolerance and replaced them. So now I am down to tubes, coils, and mica caps on the tuner sub-chassis. I have all new tubes on order for the everything before the audio stage. I've also identified all of the caps in the front end that I think could cause an FM problem if they were leaky, open, or otherwise bad. Most of these would be really difficult to replace but if it's my last hope I'll go for it. Since AM is working, I'm thinking maybe one of these caps is ok at the lower AM frequencies but fails at the higher FM frequencies.
C64 - 250pF
C62 - 750pF
C60 - 100pF
C63 - 250pF
C70 - 33pF
C71 - 1500pF
C75 - 100pF
C73 - 1500pF
C72 - 1500pF
C70 is actually a Micamold cap. I've read before that Micamolds are actually paper caps...is that true? If so I'll replace it for sure.
What are your thoughts on this plan? I'm running out of ideas so I hope someone can give me some guidance.
Thanks,
Rich
C64 - 250pF
C62 - 750pF
C60 - 100pF
C63 - 250pF
C70 - 33pF
C71 - 1500pF
C75 - 100pF
C73 - 1500pF
C72 - 1500pF
C70 is actually a Micamold cap. I've read before that Micamolds are actually paper caps...is that true? If so I'll replace it for sure.
What are your thoughts on this plan? I'm running out of ideas so I hope someone can give me some guidance.
Thanks,
Rich