that was a wonderfull expendature of about 20 minutes. left chanel mod performed, and the noise is almost 100% gone. there is a very soft hiss that a non audiophile would not hear.... for people who normally listne loud, it could easily be confused for a "black" backround. at LOW levels it is very quiet.
(rant mode on)
why the fack was this board layed-out the way it was? the HV goes from the input on the left through a rectifyer, into a cap, into a resistor, into another cap. from here a "mildly filtered" signal CROSSES the entire board right across the middle to the "ss cleansing stage" after which it CROSSES the WHOLE way back across (actually more than the dirty cross) to another cap and then half way across the board to the actual tubes.
whoever designed this amp's board could have done a mucho better job. for examples, look at the stax brand amps. even the ones of similar vintage to this one. EVERYHTING is kept well sepperated and actually marked (gasp!) the power "filtering" section actually has a silk-screened line around it and a buffer zone of about 1cm between ANYTHIGN else!
do the following at your own risk, and at risk to your likely irreplacable amp.
anyways, to do this what you do is as follows:
locate the 2 transistors above the interstage caps. there are 2.
the LEFT one (on the side of the baord with the HV caps) is the one to look at. direecetly above it is a 2-k-ohm resistor.
flip the board over and find the TOP of that resistor (closer to the back of the case)
from here you will see an "s" shaped trace that parallels (fackers) one of the HV lines.
follow this trace upto the mosfet. it is the mosfet closer to the back of the case, and the pin is the pin closest to the top of the case.
unsolder the 2-k-ohm resistor.
cut the trace close to the mosfet close to the mosfet. there is a big open bit of board space, so just go to town with an exacto knife.
solder the resistor to the UNDERSIDE of the board. it needs to go in the hole CLOSER to the transistor.
solder a wire from the resistors free end to the mosfet's pin which you clipped.
NOTE: the mosfet's pin has 2 traces on it. one goes into a diferent resistor and diode closer to the top of the board, dont cut this one.