[NostalgiaRadioTime]

Just finished up a 1936 RCA T7-5. Total recap, resistors checked & replaced as needed. Crumbling wire replaced. It was pretty straightforward, and started to sing immediately after the work was completed. An alignment brought in even weak stations across the dial, including across the short wave and police bands.

I had it playing out of the cabinet for 3 days on the bench while working on other projects, and waiting for a repro dial scale from Radio Daze. Yesterday, the dial scale arrived, which I installed, and put it all back in the cabinet. Again, it played great. I turned it off after about 45 minutes, went upstairs and had some dinner, and after I ate, I went back down with my camera to take some pictures of it. I turned it on, and had it playing for about 5 minutes. When I turned to pick up the camera, all of a sudden Diana Ross stopped singing in mid song. I thought the local station lost power....something that happens not too infrequently. So I tried tuning to a different station. NOTHING. Absolutely nothing across the entire AM band, save for a little bit of static at the very low end of the dial. So I flipped to the short wave band. It worked as it did before....had Mexico, England, Japan playing. I then flipped to the police band, and even got a few stations on it. So I determined the other two bands are working fine, but the AM band suddenly went dead.

I started at the beginning...the most obvious, although I didn't expect it would be that simple. But one by one I tried swapping with known good tubes. As I figured, it made no difference, but at least I can safely rule out that it's NOT a tube.

I lightly blew some compressed air into the variable capacitor, thinking maybe something fell between the fins, but that didn't help either. Nor did cleaning the band switch again. So now I'm to the tracing wires stage from the band switch, but I wonder if anyone else has experienced something like this and can help me zero in on what could be the culprit? What would suddenly cause the AM band to go dead? It almost acts like a coil opened. Here's the schematic:

http://oldtech.net/RCA/T7-5/35P390.gif

And here's the wiring diagram:

http://oldtech.net/RCA/T7-5/35P391.gif

Thanks,

[mikethedruid]

First thing I'd do is ring out the coils used in the BCB circuit. If they ring out OK, then I'd try replacing the small value mica caps used in that part of the circuit one by one. Of course, it could be something as simple as a cold solder joint in one of those circuits too. That is where I would begin looking. Hope this helps.

[Radioroslyn]

Would take a listen for the oscillator in another set. Clean the band switch. Wiggle and or replace the mixer tube.

GL
Terry

[NostalgiaRadioTime]

Success! I gave the band switch a more thorough cleaning, re-soldered about a dozen connections (just let the solder flow more with heat), and then held my breath. The AM band worked again as before. So while I can't say it was just the band switch or any single solder joint that caused it to cut out, I'm convinced it was one of those things. I breathed a sigh of relief when I realized it wasn't a coil. After that model 89 a few years back I break out in a cold sweat whenever I find an open coil!

So I was finally able to take those pictures I set out to do Friday night... my cell phone doesn't take the greatest of pictures but I wanted to snap a few while I had it playing on the workbench....

   

   

Radio Daze did an excellent job reproducing the dial scale....

   

Thanks to everyone for their suggestions. I sincerely appreciate the help

[mikethedruid]

What a beautiful old set ! With the RF stage I am sure it is very selective and sensitive; those old RCA sets were; and, with complete coverage from 550 Kc to 19 Mc you'll have a lot of fun. Congratulations !

[klondike98]

[Fred Taylor]

Very nice

[Scott D]

I know this is an old thread, but thanks. I'll start work on mine next week Sept 2021. Always helpful to learn what is finicky about these sets.

[radiorich]

Hello Greg,
nice job and I know first hand some of these radios can have issues like that !

Sincerely Richard

[NostalgiaRadioTime]

Funny seeing this pop up again. I sold the radio 2 or 3 years ago. Oddly enough I could have bought another at our last WARCI meet on the 12th but ultimately passed on it.

[Ron Ramirez]

I still have mine. I put so much work into restoring the cabinet, which was a wreck, that I doubt I'll let it go anytime soon.