[GreenKeys] 120VDC power supply noise?

[Eugene Hertz]

hello all,

from a fellow greenkeyer, I received a 120VDC power supply that was used for TTY equipment (has 2 1/4" jacks wired in series with a big current limiting resistor).  It is a very basic circuit. Has AC into the primary of a transformer, secondary has a 440VAC 4MFD capacitor on it. Then the secondary runs to 4 germanium diodes in a "stack" or so they term it in the circuit diagram. Finally, the output has another big capacitor (for ripple smoothing) and a bleed resistor across the cap.

Here's the question When I plug this in, it makes a REALLY loud 60hz buzz. This is from some kind of physical vibration, not EMI.  

I tried disconnecting the AC capacitor and that did not change anything. I tried disconnecting the DC capacitor and again, no change. To test the transformer, I placed a screwdriver on the frame of the transformer and tried to feel for vibrations in the handle of the screwdriver.  Nothing.  

The only thing left is this full wave bridge rectifier using these 4 germanium diodes. The 4 diodes are placed in something that looks like a heat sink of some kind, where the diodes sit in holes in the fins of this thing. Almost looks like a selenium rectifier, but this has distinct diodes. Using my screwdriver test on one of the fins, I seem to feel a light vibration.

Could this be causing the noise? Has anyone else seen something similar? I will probably replace with a standard silicon rectifier from rat shack. 

Oh, by the way. What exactly, does the AC capacitor do? (the one connected across the secondary of the transformer, it is rectangular and is a little taller than a pack of cigarettes.

Thanks
Eugene