There are bolts through the laminations on the transformer. Tighten
them, they should reduce the hum. Some transformer cores are destined to
hum because at high flux densities, the iron changes size
(magnetostriction its called). But often tightening up the core and
dropping in some transformer varnish helps corral loose laminations.
Making sure that the transformer's external field isn't shaking the
steel case is important for quiet also.
Aluminum electrolytics do get poorer with age. Replacing them won't hurt
and may help the transmitted signal quality. Especially if the amp has
been sitting unused. They age much more rapidly on the shelf than when
being used. I won't accept new capacitors more than two years old and I
prefer them to be under one year old.
73, Jerry, K0CQ
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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