This is not quite a tube issue but I think I can help you. The offset
voltage adjust is set to borderline operation. i.e. there is approximately
50mV at one of the speaker outputs. Yamaha had two pots per channel for
adjustment. One was for idle current and the other for this offset adjust.

Your speaker protection circuit is sensing this offset and turning on and
off depending how bad it is.

Carroll
wrote in message
oups.com...
I have a Yamaha R-900 Receiver that has worked flawlessly up until
about a week ago.

About one out of four times that I switch it "on" the protective
circuit relay does not engage.

Also, if I leave it on for several hours, the receiver will shut down.
Any suggestions?

Thanks,

Mark