[Amps] buzzing Drake L-4B power supply

[k8bb at comcast.net]

Oh gurus of many watts ... I have searched the archives of wisdom but do not 
see any reference to an L-4B with a power supply buzz.

I recently picked up this very nice old Drake relic. The amplifier if quite 
clean and functions flawlessly. (You know ... only driven by an elderly 
gentleman on early Sunday mornings ... )

However, after having been on for a bit yesterday and while helping bust 
through 12m and 10m pileups on VP6DX, the power supply developed a buzz - a 
"bright" sounding 60Hz buzzing that could not be ignored. Switching the high 
voltage to low (CW, 1900v) seemed to make the problem go away; returning B+ 
to high (SSB, 2400v) made the buzz come back. I tried the usual "gentle 
tapping" on the power supply case and checked to make sure all of the 
external screws were tight. Then, I cranked up the volume in the headphones 
and didn't pay serious attention until the QSOs were in the log. Later, the 
buzzing was present even in CW mode and switching to SSB just made it worse.

I relocated the power supply to the floor behind a file cabinet, but the 
raspy buzz is just as loud and clear as before - an unacceptable solution. 
(I have, however, successfully solved noise problems in my truck by turning 
up the stereo and/or using earplugs.)

Help! If anyone can point me in the right direction, I would be most 
appreciative. (I do have some experience with amplifier repair and safety.) 
I did check to ensure that the signal the amplifier is producing is very 
clean and free of any 60Hz crud.

Short of a solution, I can offer a clean 80m-10m amplifier for sale to a ham 
who is hard of hearing.

73!
Don Chisholm, K8BB
Pontiac, MI
(248) 451-0545