Peavey Classic VTX problem

[dylan08]

I have a problem with my peavey classic vtx 212. I was googling stuff about the amp and i found multiple threads on this forum about problems with it, so I thought this would be a good place to ask. So my amp sounds bad. When you play there is no sustain and the sound is very low and fuzzy. One of the capacitors looked like one of the leads had broke and the previous owner fixed it with wire so i replaced it. I thought the tube sockets may have been bad because the amp is about thirty years old. Replacing the sockets did nothing. I don't really know what to do. When i plug into the power amp in it sounds the same, but if i plug into the normal input then plug a cord into the pre amp out and into another amp it sounds fine. So i think the problem is in the power section. Any ideas?

soundcloud.com/dylanmn/straight-in this is what is sounds like. I made this recording awhile ago for a thread on another site but i didn't get much help.

[Enzo]

Just for science, plug a cord into the power amp jack, and at the free end, measure for voltage. We don't want to see 15v there. Do we?

You have two power tubes. You have changed tube sockets and capacitors, but have you tried a good set of 6L6s?

Verify voltages. Is there B+ on BOTH plate and screen pins of BOTH sockets? Is there about +15vDC on pin 5 of both sockets. And is there within 10 volts of +85vDC on pin 8 of each socket?

[dylan08]

I changed the tubes, so they should be good. I'll check the voltages tomorrow. but if the voltages are good, what else should I check?

[nashvillebill]

Fortunately for you, Enzo is "the man" when it comes to Peavey stuff and he knows this amp well. Measure the voltages as he asked...you do have a schematic? Peavey can email you one, call them and they will fix you right up with a schematic.

This is a great amp when it is in good condition. It's well made and simple to work on, and the components are still readily available. And you gotta love the socketed IC's, makes repair a breeze.

[audiopete]

I spent a week in Meridian at Peavey for Media Matrix training and met Hartley and Joe and they are top notch people with a great organization who I have a ton of respect for. They more than took care of us the entire week and showed us a great time. Their service support is excellent and that is important. Also I would love to get a VTM60 one day. Loved them since the first time I heard one.

I would have to agree by the sheer size and scope of Enzo's contribution here that he is, in fact, the man.

[Enzo]

Then you know PV is commmitted to support, and they have great peole like Gene Ford and others there who can also provide individual assistance if we don;t manage it here. Haven;t seen a Peavey product I couldn't fix, though.

[drewl]

Strange coincidence.

Just rebuilt one of these the past two days, with the help from some great threads I found here.
The cathode drive transistors were shorted as well as the little TO92's before them.
Used some 15032's, replaced the bad output tubes and it's sounding great.
Also had to replace both quad op-amps to repair the phase circuit.

The phase sounds very good, I was going to see if anyone ever built the phase circuit into a pedal?
Pretty easy and sounds great.

[audiopete]

Joe Peavey gives out his personal email and tells people to use it anytime. That guy is brilliant - he did all the Media Matrix programming.

[dylan08]

I just checked the the voltages, on both sockets pin 5 was 15vDC. On one of the sockets at pin 8 it read 95vDC so I guess it is good because it is within 10volts of 85vDc. But on the other socket i couldn't get a reading at all at pin 8. could this be my problem? what should I do?

[Enzo]

OK< a pet peeve of mine. "No reading at all." To me that means your meter went blank. If you mean zero volts, then please say you got a reading of zero volts, not "no reading." This especially bothers me when people say it about resistance. If they say they got no reading on a resistance scale, do they mean no resistance as in zero ohm, or do they mean no reading as in open circuit? regardless, zero is still a reading.

If you got zero volts on pin 8 of that power tube, then either the tube is not conducting current at all, or the cathode is shorted to ground - meaning most likely the cathode transistor is shorted for that tube.

Power off. Discharge things. Measure resistance. Is that bad pin 8 shorted to ground? Are either of the tube drive transistors shorted?

[Enzo]

OK< a pet peeve of mine. "No reading at all." To me that means your meter went blank. If you mean zero volts, then please say you got a reading of zero volts, not "no reading." This especially bothers me when people say it about resistance. If they say they got no reading on a resistance scale, do they mean no resistance as in zero ohm, or do they mean no reading as in open circuit? regardless, zero is still a reading.

If you got zero volts on pin 8 of that power tube, then either the tube is not conducting current at all, or the cathode is shorted to ground - meaning most likely the cathode transistor is shorted for that tube.

Power off. Discharge things. Measure resistance. Is that bad pin 8 shorted to ground? Are either of the tube drive transistors shorted?

[dylan08]

where are the cathode transistors?

[Jazz P Bass]

Q6 & Q7?
On the main board, behind the reverb pot.
TO220 packages, laying down.

[oc disorder]

Have you seen this post ?
http://music-electronics-forum.com/t16601/

Quite a lot of info there

[dylan08]

I checked the transistors. The one to the tube with the bad pin 8 gave a very low reading, while the one the other tube gave a high reading. Does this mean the transistor is bad?