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Re: How do I forward bias my B&K ST 140?

Posted by Dan on April 15, 2003 at 16:50:34:
Hello!
What vintage of ST140 do you have?
I have one out of the late 1980's with the
toroidal transformer and 105 Watts into 8 ohms.
I turned up the bias from somewhere around 140-150
ma to 225-250 ma with improvement. There is a pot on
each circuit board (closer to the output devices) that
controls the bias. Be sure to have a DVM hooked up to
monitor the level of bias!!! I also recoated the TO3 output transistors with a heavier coating of heat sink grease, and
also tightened the screws that hold the transistors in place
(but not super tight!) I also leave the top lid off the unit.
The temperature of the transistors (MOSFETs) does not go up
all that much if you do the mods I mention above. This can
be a great sounding amplifier for the money with some tweeks
to wiring, capacitors, bypassing, damping, etc.!
Dan