I'm restoring a 42-350 I've recapped and all tubes test strong except the two 7v7's. All tube voltages seem to be within specs. My problem is low volume. After rechecking my recaped connections to make sure I didn't make any mistakes I discovered I have plenty of volume in push button mode. I've tried cleaning the band switch with contact cleaner and tried to scrape the brass where I could to make better connection. It doesn't look corroded.
Is there a way I can eliminate the band switch as my problem? What other problems can be causing this? I feel I have tunnel vision now as I feel the band switch has to be the problem. Can it be the weaK 7v7 tubes? I have another 42-350 with a bad transformer, but guess what? Every tube but the 7V7's.
Thanks in advance.
Hi
I'm studying the 42-350 schematic.
Are you getting normal volume only in pushbutton mode? What about the SW band, is it also weak?
If you are getting normal volume in pushbutton mode, then don't worry about the 7V7 tubes. They are the IF amplifiers and should not have an effect with this problem, which appears to be limited to the front end section.
Scraping the band switch terminals is not a good idea as there is a chance you could damage the switch. Try CAIG DeoxIT instead. Great stuff! Expensive, but worth every penny. It has brought switches and pushbuttons back to life for me that regular "contact cleaners" would not help.
From my analysis, let's say your "low volume" is on the AM band only. That would point to trimmer (15A).
If it were SW only: capacitor (18 ), trimmer (15B).
But don't start replacing components yet.
Have you aligned the radio? This may be all that it needs.
Volume is better in push button mode, but I feel it could be louder. Definitely louder in push button than tuner. Yes I did an alignment. Didn't try the shortwave. Will have to wait till this afternoon to try your suggestions.
Thanks for the help.
Ok I re-alined, rechecked all voltages shown in schematic they are all within 2 to 3 volts. Looks like only plate voltages shown. Not knowing what to do next I injected a weak audio signal into the grid of 7B5 and got a good strong return from the speaker.
I'm a newbie so please bear with me. I'm thinking now I have a RF or reception problem. Still have better sound/reception on push button than manual tuning. Of course I have both set for the same local station. I checked all Band switch connection that I could find on drawing for position 2 broadcast they all showed continuity in the ohms range. While I was doing this I discovered if I touched the #1 lead of (10) the broadcast aerial trans. reception/ volume increases 100%. But is still lower in manual that push button tune. Push button sounds almost normal with a length of wire attached to this lead. By the way I can only receive 2 stations on SW and they are barely audible. I don't usually give up easy, but there has to be less aggravating hobbies
All suggestion and comments welcome.
Thanks
Found 1 bad solder connection from previous repair on band selector wafer C. Reception is identical on push button and manual tuning now. But only static on shortwave. going to concentrate on band selector switch by comparing continuity on each band position with identical spare parts chassis. Will update.
Thanks again.
Good to hear you fixed your AM reception!
Check the SW antenna and oscillator coils for continuity, also.