[Collins] humm

[Dr. Gerald N. Johnson]

On Fri, 2009-04-10 at 09:48 -0400, drleborgne at aol.com wrote:
> Dear Collins aficionados;
> ?My 32S-3 has a humm probably coming from pwr supply. I checked original filter caps and look OK.
> Should I replace them anyway???????????? Regards :Martin

Yes. Including the one on the bias rectifier. Visual inspection won't
detect high series resistance that old electrolytics develop.

Its also possible for hum to come from tubes with heater to cathode
leakage. That will make the hum 60 Hz sine wave, while faulty
electrolytics cause the hum (except from the bias supply) to be 120 Hz
sawtooth. Bias supply hum will be 60 Hz sawtooth. And if the bias supply
rectifier is a selenium (little Sarkes Tarzian rectangular module) it
needs to be updated to a silicon rectifier (1N4004 to 1N4007 appropriate
mounted on a two insulate terminal strip).

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer