UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Cretinous idea

Diabolical Artificer · 11th Oct 2019, 4:48 pm

After trying to trace a hum/noise issue on a guitar amp, looking at all the usual potential areas like layout of AC heater wires, grounds, possible htr to cathode SC's etc etc, I found the problem - the combined pot and mains switch.

Never occurred to me before, but thinking about this, it is a monumentally stupid idea to put a source of high voltage AC right next to a pot that often connects straight to the control grid of a high gain IP stage. I mean why bother laying the heater wiring into the corners of the chassis and wiring the valve socket heater pins properly, keeping the mains tfmr away from the OPT and orientating it 90 deg, etc, etc and then plonk 240v RMS 1/8" next to the wiper and wire that goes to the grid. Madness.

Andy.

11th Oct 2019, 4:48 pm	#1
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Cretinous idea - The combined volume pot and mains SW. After trying to trace a hum/noise issue on a guitar amp, looking at all the usual potential areas like layout of AC heater wires, grounds, possible htr to cathode SC's etc etc, I found the problem - the combined pot and mains switch. Never occurred to me before, but thinking about this, it is a monumentally stupid idea to put a source of high voltage AC right next to a pot that often connects straight to the control grid of a high gain IP stage. I mean why bother laying the heater wiring into the corners of the chassis and wiring the valve socket heater pins properly, keeping the mains tfmr away from the OPT and orientating it 90 deg, etc, etc and then plonk 240v RMS 1/8" next to the wiper and wire that goes to the grid. Madness. Andy. __________________ Curiosity hasn't killed this cat...so far.