Yeah there's a local amp tech I know around here, he's kind of a dick though and basically tells you to buy a new amp if you have a Peavey.  He did that a couple years ago when I had asked him about my Heritage VTX and told him what was going wrong with it (turns out it needed new filter caps).  But yeah he had told me it was a junk amp and that he was working on one not long before that "it was designed by some crackpot engineer who decided to make and amp that doesn't make any sense and blow tubes every 10 minutes."  Said he wasn't even going to finish working on the other guy's amp and told me to sell it for parts and buy something better like a Mesa or a Hughes and Kettner.

Well it has an output transformer like a tube amp would, to give it a more tube-like tone I guess.  Peavey called it an auto-former when I asked for a quote on the price when I asked them incase I needed to replace it ($78 btw).  I guess because it's an output transformer that's switchable on wattage, not sure how it all works.

Seeing as is it was a long distance transaction that's not an option lol.  I guess I can always throw and attenuator at it to drop the volume without losing the tone.  You can't just turn the volume down on the master volume on the XXL, your sound just turns to garbage.  Either that or run a good pedal into it when I need to play it low.  I just thought it'd be nice to fix it if I could figure out what's going on with it. 

Oh and the speakers are good, that's what plugged into the VTX.  I figured I'd fix the XXL and if I liked it with the proper power section I might even sell the VTX and buy a speaker cab or two to go with it.

I dunno what the VTX goes to on low power, i know on high power it's 130W.  That isn't the point though, the point is I want to fix the head.  But yeah even on the low power mode it's real loud and if I want to play at night and not bother roommates even 22W of tube power would be way too much.

So I scored a Peavey XXL head for $75, but the kicker is there's something wrong with the power section.  The guy I bought it from said a tech quoted him $60 to fix it so I was hoping it's nothing too major like the autoformer that's in there. I've not really worked on solidstate heads much so I'm going to need some pointers on what's up with this.  The preamp works fine, I'm running it into my Heritage VTX's poweramp (which I just fixed prior to getting the xxl  :tu: ) at the moment. It sounds good through it, but I would like to fix the head due to the fact that it has this nice power switch on the back so I could kick it down to 25watts to practice in my bedroom late at night.  Here's what's going on though.  It doesn't output any sound through the speakers.  When I turn the volume up all the way and set it to the ultra channel though I can hear it very very faintly playing (and whining type of sound), but not through the speakers, something in the head itself possibly the autoformer? I don't know if that's possible but yeah that's what's going on, seems really odd.  Any ideas from anyone out there?  I've got no clue where to start.  Usually checking the fuses is the first thing if there's no sound I thought, but they're all fine.

I got lucky, only one of the smaller caps actually needed replaced and I was able to get it at radioshack for $1.60  :tu:.

Well I got the tubes in.  What I thought was noise from bad tubes apparently isn't  .  The transistors fixed the tube red lighting problem, but I'm wondering if maybe the filter caps were killed off too when everything happened  .  I had swapped them out a year and a half ago so it's kind of a bummer.



Uploaded with ImageShack.us

I was running some Sovtek 6L6 WXT+ tubes in there and they held up great until those transistors went out.  I may get another set of them.

The new transistors fixed it, other than the tubes which are all bad and sound god-awful.  Looks like I'll be ordering some tubes soon.

Also, in case anyone else needs these, there's a site  www.tubesandmore.com that has them with the original parts numbers.

just search SJ6465 and MPS 6531

The resistors check out to the proper ohms as marked.  It's one of the transistors.  Q7 is bad.  I'll just go ahead and replace them all like you recommended, they're 25+ years old after all.

Quote from: J M Fahey on July 10, 2010, 11:49:31 AM
In this particular circuit (which is not like any other tube amp, except the Music Man) , the bias is *always* being adjusted automatically, no matter what the tube, new or old, because it has a SS servo bias circuit.
The tubes will always pass whatever current the cathode-driver transistors feed them, until they die suddenly at the end of their life.
Their grid, in fact, always has +15V (+24v in MM's) and their cathodes will float to whatever voltage is necessary to pass the current fed by the drivers.
Those redplating ones either had some internal short or whatever *or* were fed too much current by a malfunctioning drive circuit.

You're right, with this amp you pretty much just stick whatever 6L6 types of tube in there.  I've never had an issue with any tubes in it.  The only thing besides tubes that's been changed over the years is the filter caps which I changed last year.  The previous owner had it since the early-mid '80s.  He even gave me the original tubes that came with it which were still working.  I haven't been able to test anything because I couldn't find my multimeter and I've got too many other things to pay for to really spend any more money until I get paid at the end of the week.  I'll have an update on what went wrong or if I run into any problems.

Now I just need to find my multimeter...off to the garage to look through some boxes (gotta love moving, right?).  I'll have to check it out tomorrow and report back what I figure out. Thanks guys!

Uploaded with ImageShack.us

this pair here?