Help! My P2 has started humming quite noticeably on both channels.
The hum varies with the volume control, and is audible during quieter passages at normal listening levels.
I’ve tried switching valves out one at a time, also removed the 5687 and the 2 OA2s - no change. I’ve also just checked the circuit dc voltages against @murrayjohnson’s chart and all are in the right ball park, but all are about 5-10% low. Also tried adjusting the PSU trim pots and the voltages across the 180R resistors connected to the anodes of the 5687 are both around 3.5V, not quite the 5V I’d like, but should be ok. The P2 hasn’t been monkeyed with as far as I can tell, apart from the heater circuit bridge rectifier that I replaced about 18 months ago.
I’m suspicious of the (original?) PSU capacitors but running out of knowledge and ideas - can anyone offer some advice on where to go next?