Peavey Classic 30 Not Switching Channels

[dorrisant]

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

[Jazz P Bass]

The channel switchong relay works off of the -36Vdc bias supply.
What that has to do with the preamp tubes, I do not know.
Attached schematic may help.
I would monitor the -36Vdc source going to the relay & try to see what is going on when you insert the preamp tubes.
Maybe you could pull the header that goes to the footswitch jack, to remove that from the equation.
The only other -36Vdc connection that I can see is for the reverb Jfet.

[Jazz P Bass]

To add: the -36Vdc supply also gets knocked down to the -30Vdc & -15Vdc supplies.
As far as I can see, the -30 is used on a transistor for the FX loop & the -15 is used for the reverb opamps.

[g1]

The filaments run off the same winding as the -36V is derived from, so something must be pulling too much current.

[Jazz P Bass]

Thankyou G-one.
I have worked on these amps but that one eluded me.
Enzo I am not.

[g1]

Enzo I am not.

Well get on it man!
He seems to be stalking the joint, but no posts .

[52 Bill]

Well get on it man!
He seems to be stalking the joint, but no posts .

No one here will ever replace Enzo! I hope all is well with his new lifestyle.

As for the amp, I've had problems with the footswitch jack and connecting wiring on these. The normally closed switch contact in the jack completes the ground circuit for the relay coil. Try cleaning the jack and the internal push-on connector.

[Randall]

I miss Enzo.

[dorrisant]

Figured it out... The relay had been replaced with the wrong type. I pulled it out and checked to see if it was switching... it was. All contacts were fine. I measured the coil resistance and checked against another relay from a Delta Blues... Supposed to be approximately 750 ohms but this one was reading about 250 ohms... That would be roughly 3 times the current draw. I replaced it with the correct part number and now it switches fine.

Tony

[bsco]

Well get on it man!
He seems to be stalking the joint, but no posts .

He is probably sitting back with a glass of nice wine, smoking a Cuban cigar and
getting entertained by us techs.....more power to him!!

[bsco]

Figured it out... The relay had been replaced with the wrong type. I pulled it out and checked to see if it was switching... it was. All contacts were fine. I measured the coil resistance and checked against another relay from a Delta Blues... Supposed to be approximately 750 ohms but this one was reading about 250 ohms... That would be roughly 3 times the current draw. I replaced it with the correct part number and now it switches fine.

Tony

Somebody probably installed whatever relay they had on hand instead of sourcing the correct one.........I very recently saw a Marshall that had 4 resistors tied together to get the value required.....so anything is possible....on a brighter note.....I find that these types of repairs teach me alot.....and that is "Anything is possible"

[audiopete]

Somebody probably installed whatever relay they had on hand instead of sourcing the correct one.........I very recently saw a Marshall that had 4 resistors tied together to get the value required.....so anything is possible....on a brighter note.....I find that these types of repairs teach me alot.....and that is "Anything is possible"

Also, "what not to do"