Peavey Classi 30 cuts out

[brewback]

This amp has had the tubes replaced and is dropping out. The power tubes are turning off. Sometimes at a cold start they don't turn on. Sometimes in the middle of play they just turn off.

Any clues? Rectifier?

Rick

 

[jazbo8]

Are the heaters wired in series? If so, perhaps you have a bad tube. BTW, you are in the wrong forum...

 

[MadsKaizer]

How fast are they turning off?

Instantly: look at the plate supply, signal line, loose wire

Slowly turning off, lower sound level, distortion: look at heater supply missing

Sounds more like a loose wire to me

 

[MelB]

Found a schematic. Yes they are in series. You have a bad new tube possibly. Do you still have the old set of tubes? Try them again if you do.

 

[Tesla88]

Schematic for reference

Lose wire or a bad tube or tube socket . . .

http://elektrotanya.com/PREVIEWS/63463243/23432455/peavey/peavey_classic_30.pdf_1.png

 

[boobtube]

All these are good suggestions, also could be a cold solder joint making intermittent contact with heating of the circuit. You could have loosened a solder joint for the tube sockets when removing or replacing the tubes. This is a printed circuit board amp, so this is also likely.

 

[famousmockingbird]

I have one of these amps right now all opened up for similar issue, the amp has multiple cold solder joints on each power tube socket.......even the preamp tube connections look bad. I removed all the old solder and resoldered the tube sockets.

On a side note I might be starting a seperate thread about these amps, I have found a couple of strange RC networks on the normal channel before the signal even gets to the tone stack. R8 and C9 cut the lows and I believe the local feedback around V1B attempts to tame the highs Seems like confilicting tone control but maybe my foggy brain isn't seeing things correctly. I plan to put more time into making the clean channel sound a little better than it does. I think it has potential but even after a speaker change the highs are just too ice picky for me.

 

[Enzo]

Intermittent heaters in the EL84s would be pretty rare.

The tube heaters are in series. If you look at the schematic, there are a couple of resistors in series with the string. They are on one of the three boards, while the tubes are on another, and the power comes into the third. If you look at the two resistors, they are wired to short bare wire jumpers over to the other boards, two at each end. The little jumpers can crack and break, the resistor solder can fail, the jumper solder can fail. Those are the most common causes of your symptoms. Look especially for discolored solder in those areas, when the connection fails, it often gets hot, further degrading the joint.

Whenever you are inside one of these amps, it is a good idea to gently tug on each and every small bare wire jumper to reveal if any others are broken.


The Classic 30 is a fine little amp, very popular. yes, it is better to start a new thread to discuss its circuitry so as not to confuse this repair. If you go to BlueGuitar.org there are a bunch of modifications that have been done to this amp, you may pick and chose from those.

 

[brewback]

Thanks folks- tubes seem fine- time to get under the hood!

 

[famousmockingbird]

Here is the Classic, here you can see I had resoldered V7. Pin 2 on V6 (circled in green) cleary has a cold solder joint. Like I said, every tube socket on this board had cracked joints.
​

 

[Enzo]

And that is in fact a classic example of a cracked solder joint, a better picture I have not seen.

I wish I had some photos of the resistors I described.

 

[famousmockingbird]

I wish I had some photos of the resistors I described.

Ask and you shall recieve


Topside view I labeled the resistors and circled the jumpers in blue. Underside view I circled where the resistors and jumpers get soldered too. Hopefully this will help him sort the problem out and or future people with the same problem.

 

[Enzo]

Yes, exactly those, thank you.

Look for discolored solder or discolored wire jumpers if there are no obvious cracks.

Oh, and check the two resistors, one may have gone open.

 

[brewback]

That's awesome- Thanks! I resoldered all of the tube pins and also found one of the wires that connects one board to the other was loose from folding. Sounds like it did the trick. 10hrs or so on and off and not troubles!