Peavey Classic 20 Power Tubes Won't Light...

[Roverjoe]

Hey guys- I'm new here and I've got a question about my Peavey Classic 20. I did some searching around and if there is another thread that would answer my question please direct me to it.

I pulled my Classic 20 out of a closet where it had been stored for about 16 years. The amp did not have any tubes in it, so I ordered new JJ matched tubes and put them in. The preamp tubes light up, but the 2 power tubes will not light. I checked all of the fuses and they are all good. Is this a bad output transformer? I used this amp to practice with my band in highschool and vaguely remember plugging it into various cabinets and had no idea of ohms, etc. I remember my settings: Master on 12, Volume on 7 or 8.

Can I check the output transformer? Can I find a replacement?

Thanks so much!

Joe

[Don Moose]

Storage doesn't do bad things to a transformer ... unless it gets wet or really hot.

By 'light up' do you mean no orange heater glow or no blue HT glow?

It's much more likely one or more of the OT's wires have come loose or their solder connections may have deteriorated (happens sometimes).

In the attached schematic, pay attention to the wires and connections around J14, J15, and J19.

Hope this helps!

[Roverjoe]

Thanks Don. I'm sitting here thinking back 16 years, and now I do remember the amp cutting out while playing. I think that's why I took the tubes out and stored it. I picked it up over the holidays from my parents house.

The pilot light does come on. The preamp tubes (ECC83s) come on and glow, but the power tubes (EL84) do not come on at all. No glow, no heat, nada. I tested and no output to the speaker at all....

Thanks for the schematic! I'm hoping I don't have to take this in....i would really like to fix myself.

[Enzo]

I'm sorry, the power tube heaters don;t come on, and we are suspecting the output transformer? What possible connection could the output transformer have with the power tube heaters?

The preamp tube heaters work, so the heater fuse is OK, and the transformer works. SO the problem is getting the 6vAC to the power tubes. I might suspect socket solder, but not on both tubes. SO I am drawn to the little jumper wires that connect the pc board sections together.

I am attaching a pdf of the schematic file that includes the layout. Look on the left end where jumper wires connect the top pc board to the center board. Below V4. The first and fourth jumpers carry the heater current. I bet one is broken.

In fact, as long as it is open, go down the row of jumpers. Well, two rows actually, since there are three boards. Get under each jumper wire and gently but firmly tug on it. If any come free, they were broken - fix them.

Avoid as much as posssible flexing the boards, bending those jumpers can break them off.

[Roverjoe]

Thanks Enzo, I appreciate it - I am going to inspect all of the jumper wires right now. How do I gain access to the PDF you have attached?

[Enzo]

I am an idiot. I lined up the drawing then forgot to add it on.

Here:

[Roverjoe]

Fixed it! Thank you so much for your help! Was a broken jumper wire right beneath one of the fuses.

Wow, these JJ tubes sound great! Time for a replacement speaker now.

Joe

[lmolter]

Roverjoe, I picked up a Classic 20 over the summer and had to replace the volume pot. What a pain that circuit board is. Anyway, mine sounds ok with the stock speaker. What speaker were you thinking of buying for it?

Larry

[Don Moose]

Thank you - complete diagrams are so much more useful!

[Enzo]

They used that god-awful circuit board setup on the Classic 30 and the 5150 Combo amps as well.

[rockon1]

Another one fixed with your knowledge Enzo. Bob



http://www.thegearpage.net/board/sho...d.php?t=490145

[Enzo]

Tell the guy it is from vibration. The boards vibrate around in there from the speaker being nearby. The wires can break.

This same exact board layout would not be breaking jumpers if it were just a head. (No speaker.)

[peaveyfixer01]

Thank you!!!

I had the exact same problem with my Peavey Classic 20 (also recently pulled out of storage) and found this thread searching the internet for repair clues.

I subsequently joined this most excellent community (so I could download the circuit diagrams) took my amp apart (stupidly got shocked before I remembered that I should discharge all the capacitors before poking around), and found the broken jumper in question. On my amp, J410 (If I'm reading the numbers correctly) which is right next to F2 was loose, and luckily I could access the junction without doing any disassembly. I just soldered the repair 15 minutes ago, and am happy as a clam that the amp works again!

One additional modification I made was to bridge the two circuit boards together with some epoxy in the vicinity of J410, which will hopefully stop the boards from vibrating so much, and stop the connection from coming loose again in the future!

Anyway, just wanted to share my experience, and give a big THANK YOU to this community!

[Commander]

Thank you so much for all the help, after a lot of mucking around looking ito my 5150, I was about to yank my hair out when I finally found this post. I had a look at the jumper and sure enough, baked to the bone. So bad, in fact, one pin came off the board and part of the rear circuitboard's metal contact got removed too, so the pin has nothing to stick to and won't make contact with the board. I probably can jerry rig the board and pin since I am handy with a soldering iron, but the jumper plug is completely BBQ'ed. Where does a guy get that cable thing anyway, can it be ordered? Also, if I can't fix that board circuitry, am I hooped for good or can that be swapped out too? It doesn't seem to come loose without doing something with the power tube sockets, almost like they need to be unsoldered from the board. Any hints?

Thanks in advance,
TJ

[Enzo]

If the ribbon cable is burnt, bypass the burnt parts by running a hardwired piece of wire from board to board. Bypass the burnt part. The burnt trace comes from somewhere, and it goers somewhere. Just connect those somewheres together with a wire.

I rarely have to remove the power tube board from the amp. I can almost always do whatever it needs from the exposed side. Yes, if I must replace a screen resistor, I install the new one up on the solder side.

But if you just HAVE to pull that board, you drill out the 8 rivets that mount the power tube sockets. 1/8" drill. DO what you need to do, then reinstall the board using 8 new pop rivets. ANy hardware or home center store will have 1/8" pop rivets. 1/8" grip range is probably long enough. And you need a pop rivet hand tool to set them. Not expensive.


Don't unsolder the socket legs, because you will spend the rest of your life trying to get all those legs back in the holes at the same time.