"Antonio Vernucci" wrote in message
...
Most of the strong AM signals received on my National HRO
are affected by hum.

I put a ceramic capacitor in parallel to each of the
80-type vacuum diodes with no noticeable improvement. Does
anyone remember which other cure was proposed to solve the
problem?

73

Tony, I0JX

Tunable hum is sometimes caused by bad bypass caps, its
worth checking. This could also be intermodulation from
something in the neighborhood especially if these are strong
signals. Can be checked by using another receiver,
preferably a battery receiver. Someone else mentioned hummy
tubes, also worth checking.
Putting a ceramic in parrallel with the filter caps may
help but I think its more likely a decoupling or bypass cap
has gone bad.


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Richard Knoppow
Los Angeles, CA, USA