I'll look over the schem when I get a chance - but I have seen bad eyelets
at the power transformer boards on Pioneers, a bad eyelet at the center
tap would let the ground "float" and could cause your problem.

Mark Z.

Mark,

Thanks for the reply. I did check the center tap wiring it is OK. The ground
is not floating relative to power supply rails -- both high and low voltage
rails stable and correct. The power stage ground is offset relative to the
amplifier signal ground. It is a kind of weird "floating" ground power stage
power supply scheme.

If you have scheme in electronic form, could you please send it to
(remove at@ and dot.)?

Thanks,
Anatoly