[Hallicrafters] S-38 BFO and hum problem

[Kenneth Laine Ketner]

You might compare lead dress with those that don’t hum. Sometimes in
Sams or Rider’s schematics, a manufacturer will give crucial lead dress.
Check all nuts and bolts for tightness - one section of a chassis can
electrically connect to another section through what appear to be only
mechanical points. Look at crucial ground points - sometimes those will
corrode and while tight, still not good connections. I have had success
with such troublesome hummers by soldering some hook up wire to chassis
edges then soldering the other end to the suspected ground lug.

Tube swapping is good, to check for the possibility of heater to cathode
hum. My tube checker won’t catch some weaker shorts of this kind.
Sometimes different brands of tubes won’t work.

Another good tip relevant here is at http://antiqueradio.org/safety.htm
.

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Ken Ketner
ARS KA5ELD (Extra Class)
  Personal Webpage: http://www.wyttynys.net
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Email:
 home: ketner at arisbeassociates.com
 office: kenneth.ketner at ttu.edu

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