I've just completed electronics restoration of a Westinghouse WR-217. All paper and electrolytic caps have been replaced and all out-of-tolerance resistors replaced. A full alignment using a signal generator has been done. One other notable item is that I had to replace the antenna coil with a tunable universal coil. All voltages are close to stated voltages.
The radio receives plenty of stations BUT the audio is distorted sounding like the tuning is slightly off frequency. No amount of fussing with the tuning cleans up the reception.
Where do I look next? Any suggestions will be greatly appreciated.
Thank you
Don
Pin 5 of the 41 tube is hardwired to chassis. It shows as connected to ground on the schematic. Is this incorrect???
BTW - grid voltage is -12.7v.
Sorry meant pin 4. Bias looks ok.
Double check R-3,R-8, and C-14. I'm thinking your avc circuit isn't working.
I'm reminded of a Zenith console I was working on several years ago that also had a distortion issue. After much hair pulling I noticed it used the same speaker as a parts console I had. On a whim I plugged in the other speaker and BINGO, the distortion was gone (and the offending speaker looked perfect). It's probably a long-shot, but if you can substitute in another speaker it would rule that out. Ever since that experience I keep a speaker substitution box in the shop:
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attachment=21771]
Photo courtesy of Steve Johnson: https://stevenjohnson.com/testers-misc.htm
Terry,
The AVC seems to be working properly; varies from -2.5 to -3.5v depending on signal strength.
Now for something unexpected; I knew the resistance element of the original volume control was not smooth and measured ~800K vs correct 500K.
Upon replacement, the distortion disappeared!!??
Thanks for your help.
Another question - do you know of any source for the clear plastic tuning dial cover?
Don
John,
Thanks for the suggestion. The speaker substitution box is a great idea.
Do you know the approximate field coil inductance typical of the 30's radios?
Don
Quote:Another question - do you know of any source for the clear plastic tuning dial cover?
Dialcover.com makes one for the WR-217:
https://dialcover.com/
Don, a lot of the Zeniths I've been working on lately are ~ 1000 ohm field coils.
I picked up the Ferret box about 3 years ago. Prior to that I used one that has most of the tolex covering peeling off.... looks horrible but it still works fine.