[Hallicrafters] HT-37: Thanks and one more question

[Riley Hollingsworth]

Thanks to everyone who gave me the good advice on the HT-37. I finished it
and it has full output on all bands but Ten, where it has about ten watts.
Works great on all modes. I replaced caps, tubes, cleaned bandswitch, and
replaced rectifiers with solid state.
One remaining question: transformer buzzes very noticeably, with either
solid state rectifiers or the tube rectifiers; BUT, when I bring the line
voltage up to 110 or so with a Variac BEFORE turning on the HT 37 power
switch, there is no buzz.  Why would that be ? There is even a buzz when I
turn on the power switch and THEN bring up the voltage with the Variac, but
not when I set the voltage with the Variac and then turn the rig on.  Any
explanation ?