Peavey Classic 30 Not Switching Channels

[dorrisant]

I posted this elsewhere:
http://music-electronics-forum.com/t38270/

The amp wouldn't switch channels so I pulled the relay and tested it with 12v. Works fine. I put it back in and noticed that it pulled the relay in with no tubes... One preamp tube in and it still worked... A little less audible "click" but it still changed channels. Two preamp tubes in and it still worked... Less audible. Three tubes in, no dice. No switch at all in the relay. Four tubes to go... What gives?


Tony

[tubeswell]

What are the rest of the PT voltages like with all the tubes in?

[dorrisant]

They all looked right... I think I found it. Looks like the channel switching relay has been changed... Drawing 44mA across the coil. Factory part should draw 16mA according to the data sheet. Now I gotta trace the circuit to see what the new problem is... Channel two is about 1/10th the volume of channel one.

Tony

[tubeswell]

I think I found it. Looks like the channel switching relay has been changed... Drawing 44mA across the coil. Factory part should draw 16mA according to the data sheet.

The relay comes off the same winding as the heaters, so that could be starving the filaments, which could account for the difference as you start pulling tubes out. The pre-amp tubes are DC series, so they need 36V and 150mA, and the extra 28mA draw from the replacement relay could be upsetting them. You would notice the filament voltage change too. Not saying it is mind you; you need to measure voltages all over to really work it out.

Now I gotta trace the circuit to see what the new problem is... Channel two is about 1/10th the volume of channel one.

Leaky coupling cap? Bad pre-amp tube?