This is probably a daft question, but treat me kindly. I know nothing about electrics. I've had a much loved Wem Westminster IX amp from new in around 1974. It had a good overhaul a couple of years ago and I want to keep it happy for as long as possible. The treble control doubles as an on/off switch and I've always just used that. I'm a little concerned that the switch is probably getting a bit tired and wonder if there's any advantage in leaving that switch alone and switching on and off at the wall socket. Or is this not a good idea? Also I seem to remember my old dad telling me that hi-fi amps should always have the volume turned to zero before switching on and off. Should I be doing this with guitar amps? Pic of amp attached and the schematic. Grateful for any knowledgeable advice.