Mark Rehorst wrote:
I tried adding caps across the rectifiers- no good.
I tried bypassing the main filter cap with a 20nf ceramic cap. No
good.
I tried swapping out the rectifiers. No good.
I added a 3 terminal voltage regulator, reducing the audio amp supply
voltage to about 10V. Buzz all but gone. I have to press my ear to
the speaker to hear any buzz now.

Try replacing that one cap with a larger valued cap. Or make a pi filter
with a resistor and another cap.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."