> Transformers will vibrate when voltage is supplied,
> specifically the
> windings. This can happen if the primary and secondary
> windings are not
> wound tightly. Or if the winding as a whole does not
> completely fill the
> window of the iron, and thus is a little loose, you can
> develop some
> buzzing.
Adding to that I would look closely at the choke. Chokes
virtually always have an intentional air gap, the gap being
necessary to prevent saturation by the high dc in the
winding.
Around the air gap there is considerable fringing of the
magnetic flux. If the unit has a steel chassis, and I'm
almost positive it does, the flux will vibrate the chassis.
Even the power transformer can have this problem, although
chokes are worse. The flux leakage from the transformer can
shake the chassis, and the chassis acts like a sounder
vibrating with the AC.
I'd take a well insulated rod, like a piece of plastic rod
or PVC, and push on the chassis around the choke or
transformer and see if you can seriously alter the sound. If
you can the problem is almost certainly flux leakage. The
cure can be shimming or bending the mounting legs or even
sliding a hunk of thin plastic under the core area to press
against the chassis.
Look at the chassis and things outside the transformer
first. You might use a long cardboard tube as a sound
channel. You can stick it on your ear and move the other end
around over the chassis and transformers to find the bad
area. Watch out for HV. It can kill you.
73 Tom
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