HR Deville Runway Current Problem

[Enzo]

No. TP30 is a voltage, but not the bias voltage. TP30 is a voltage that equates to tube current. The bias voltage is what is adjustable, and is the negative voltage put on the control grids of the power tubes.

Pull the power tubes, measure the DC voltage on pin 5 of each power tube socket. What range of voltages can the adjustment cause?

[Perkinsman]

No. TP30 is a voltage, but not the bias voltage. TP30 is a voltage that equates to tube current. The bias voltage is what is adjustable, and is the negative voltage put on the control grids of the power tubes.

Pull the power tubes, measure the DC voltage on pin 5 of each power tube socket. What range of voltages can the adjustment cause?

Ok, range on each tube was -46 to -55vdc.

[Enzo]

That indicates the trim pot is working, and the adjustment range seems reasonable.

If the problem is intermittent, keep the tubes out, watch pin 5 while you poke the circuit board with a wooden chopstick or similar. See if that -50v disappears now and then.

Other possibilities are loose socket pin. Look down into the empty socket pins, does either one have a pin 5 that looks like it might have spread a little - ie loosens its grip?
http://swartamps.com/tech/socket_retention/

[Perkinsman]

That indicates the trim pot is working, and the adjustment range seems reasonable.

If the problem is intermittent, keep the tubes out, watch pin 5 while you poke the circuit board with a wooden chopstick or similar. See if that -50v disappears now and then.

Other possibilities are loose socket pin. Look down into the empty socket pins, does either one have a pin 5 that looks like it might have spread a little - ie loosens its grip?
http://swartamps.com/tech/socket_retention/

I tried doing that but didn't get any results. The crackling has quieted down alot from what it originally was, resoldering the PI tube pins really helped. The tubes are old and I'm hoping new ones eliminates the remainder. We'll see, for now I'll call it good.