Arfa Daily wrote:
However, when you fit the new ones,
they may have significantly different characteristics, and require the bias
to be set.

Yes indeed. I ordered 2SC3264 and 2SA1295 as replacements.

With the amp on full mains voltage the quiescent current is heading for
300mA on that channel with no sign of stopping, I turn it off at this
point.

It turns out the adjustment I thought was bias only affects the DC
offset, there does not appear to be any way to adjust the bias.

It's a TEAC amp of a few years ago, no info at all online, not a hit.
A-919AV.

Briefly: Some sort of +/- drive comes from the input board, where the
DC offset pot is, this comes to the output board, to a circuit of 6
small transistors with a smattering of diodes and one transistor
attached to the heatsink, these feed the driver transistors, which then
feed the output transistors.

I think I should be looking for some diodes and resistors setting the
bias but I'm not sure where to look in all that!

I suspect the thermally coupled transistor is biasing it all, there are
3 parallel resistors connecting one of it's legs to base, obviously
some production trimming. I'm too tired to trace the circuit properly
just now, but does this sound reasonable?

I've a feeling this isn't going to be as simple as I thought...

Thanks again for all your help,
Alex