[Boatanchors] Two questions

[Joe Connor via Boatanchors]

As for the GPR-90, how old are the electrolytic filter caps? Did you ever replace them? Bad filter caps will give a loud hum. From the schematic, there appears to be two filter caps, each 40 mfd at 450V.
                Joe Connor
 


     On Wednesday, April 22, 2015 10:58 PM, Howard Ritter <hlritter at bex.net> wrote:
   
 

 I have two problem BAs that I’m trying to rehabilitate for eventual sale as I’m downsizing my life and home. Any suggestions?

1. A National HRO-500. This was working properly the last time I used it several years ago. Firing it up now, I get no audio and the Phase Lock light stays on at most frequencies.  Where to start?

2. A TMC GPR-90. This was also working properly when last used several years ago. Now I get a very loud 60 Hz hum in the phones as soon as power is applied. The volume does not vary with adjusting the volume knob and is so loud that I can’t tell whether there’s any audio underneath. Is this a recognized failure mode for hollow-state receivers? Something shorted in the audio output circuit? Tube? Capacitor?

Thanks for your suggestions. I’ll report back.

—howard n7exn
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