Hi, thanks for the answers now I have the service manual the problem looks like what you guys say there is just a little resistor / capacitor circuit and no doubt the cap is shorted = dc from the resistor straight to the amp. I will put this on the list of stuff to do like replacing a couple of lamps and maybe re-capping. For now just enjoying it and will give it a good internal clean etc one day.
There is also some hum (only noticeable when no music) and often some FM radio that comes thru faintly on one channel when using tape1 input. Probably contamination on the main power / selector switch?

Thanks again.