04-18-2019, 01:59 PM
So, to exclude the influence of the power wires in the pot switch to the audio signal, I unsoldered all 4 power wires and connected them together outside the switch, the switch pins now hanging free.
Nope. Still the same hum.
So, have to do more digging. Likely comes from the detector somewhere, as it is increases with the volume and really disappears if the input of the audio section of the Det-Amp is shorted or the scope is connected to it (which shunts 15 MOhms with 1MOhm).
Thought of bad rectification/filtering. Changing tubes (all tubes one by one, starting with the rectifier) yields nothing either. Caps were measured right before being put in the chassis. Scoping shows large ripple after the first cap, C22 (12V or so) but that is expected. Second pole of the filter looks clean.
Nope. Still the same hum.
So, have to do more digging. Likely comes from the detector somewhere, as it is increases with the volume and really disappears if the input of the audio section of the Det-Amp is shorted or the scope is connected to it (which shunts 15 MOhms with 1MOhm).
Thought of bad rectification/filtering. Changing tubes (all tubes one by one, starting with the rectifier) yields nothing either. Caps were measured right before being put in the chassis. Scoping shows large ripple after the first cap, C22 (12V or so) but that is expected. Second pole of the filter looks clean.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
