by EWBrown » Tue Nov 25, 2008 10:26 am
Power trannies can vibrate/buzz for a variety of reasons. The simplest and most common reason is loose laminations, and tightening the screws usually fixes this. If the bobbin and windings are loose and not solidly attached to the core / laminations, this is a more serious problem. Sometimes this can be fixed by inserting thin wood shims between the bobbin and core, or using some glue to hold it fast.
The other source of mechanical vibes / humis more common with the horizontal mount power trannies, as their AC induced magnetic field can get out and make the steel chassis itself vibrate. This is more of a problem with thin steel chassis (like most Hammond chassis), and the problem can be a real "bear" to fix.
Thicker steel, and aluminum chassis are not so prone to this kind of problem.
I have had a couple of cases with horizontal mount power trannies, in which the top end bell itself would vibrate at 60 Hz or sometimes at a harmonic (300Hz) and the fix for this was to put a piece of adhesive-backed rubber inside the end bell, if it fits inside, or else on the outside.
This can look a bit ugly, but it does stop the "ringing" rather effectively. I suppose that double sided tape and some form or metal "badge" or label would also work, and look better.
/ed B
Real Radios Glow in the Dark