Just bought a Champ 12 off of E Bay..

[quartersaw]

..and it *really* sucks! No bass, no power to speak of, no clean headroom.The seller said that the amp had Torres Jack, distortion,and bias mods. The bias on the 6L6 power tube *turned all the way down* was 44ma. I took a voltage reading off of one of the power supply caps,and it was 495 volts! I know just enough to be dangerous, but I'm really not skilled when it comes to diagnostics.
This thing is a mess,and I'm looking for suggestions as to what to do with it besides throw it out the window.

[soundguruman]

Well, file a really bad review for the seller and tell the seller to refund your money.
E bay won't do anything. It seems like they protect dishonest sellers. From my experience, anyway.
BUT here is the lesson. Buy an amp off e bay, you never know what you are getting.
I suppose that the majority of amps for sale on e bay have some type of hidden defect.
That's why you should deal with a local vendor.

[Greenmachine]

I read on another forum that if you say the thing was broken, or was not as the seller described, you can get some results. I say file the complaint and see what happens.

[g1]

First thing I would do is verify that the speaker is ok, or try another speaker.

[mort]

Ebay really does side with the buyer in most cases these days. They have even written into their policy that even if a seller doesn't offer returns, that they can be made to accept them(given that there is even a shred of a claim to "not as described"). If it was a fairly cheap buy then maybe just keep it and use it as an opportunity to learn something. I personally would look for every excuse to do the latter.

[quartersaw]

Well, the seller gave me fifty bucks back, He offered to give me a full refund, but I was only into this thing for $150 total, so I decided to keep itas a project. I just installed a Hammond 10W. single ended output transformer, thinking that would solve the problem. The amp is much louder, but still has totally crapped out bass, and still not a shred of clean headroom. I kept the amp because I like the platform of a single ended 6L6 with a 12" speaker. The stock Fender 12" speaker is O.K. I installed an RCA black plate 6L6GC, and a pair of RCA 12AX7A's. I replaced all of the power supply caps. (originals were 350V 47UF). I used 100UF 450 volt Poly caps. -Still have farty bass, and no clean headroom. The owner said that the amp had a Torres "distortion mod", Switchcraft jacks, and an adjustable bias installed. I don't know anything about this distortion mod, but the other stuff was in place.
There are two tiny diodes for the DC voltage. Might this have any bearing on the problem?
Any advice is much appreciated! I can fudge my way around an amp without killing myself, but I'm not an expert about this stuff like I would like to be.
Thanks in advance!

[mort]

Maybe just start by inspecting the circuit, comparing it to the original layout/schematic bit by bit, and then returning everything back to stock. I don't know that much about diagnostics either but that's what I would do. That way you could start from square one, and it would be easier to get help. As it stands right now, no one can really help much because they don't know what has been done to the circuit, specifically. If it was the stock circuit you could post the schematic that exactly matches your amp, post up some voltages, and go from there. Trying another speaker, different instrument cables, and/or instruments themselves is always a good idea to rule out the possibility that something else is not actually the cause of the trouble.

[quartersaw]

The B+ is 497v.(as specified on the schematic) I've got the bias corrected. I couldn't see anything on the circuit board that had been obviously altered. (I tore one of the traces soldering a cap in place) I admit that I cannot read a schematic correctly.
There are a couple of tiny caps, and resistors that are connected between the 12AX7A's that do not look original. I disconnected them (I've since reconnected them) and disabling them made *no difference* in the sound, or volume. I have a feeling that the previous owner may have goobered this thing up.
The reverb was inop, so I removed it.(Looks like a POS anyway)
All that I have to go on is whatever advice people here might be able to give me as far as what causes a headroom problem, and take it from there. If anyone would like to chime in, I'd sure appreciate it!

[quartersaw]

Anybody?
(Please?)

[g1]

This is not a simple circuit and without being able to understand schematics there is not much you can do. Just disconnecting parts you think have been added does not mean you have disabled the mod. You may have disabled the circuit.
The schematic has DC voltages (in square boxes) listed for the tubes. Check them all and post your results.

[quartersaw]

Thanks for replying! I have been really busy the for the last week(playing a gig tomorrow night), so I will get that info after the weekend.
(I hooked that circuit back up since there was no difference without it )

[loudthud]

That amp uses a voltage doubler, so 350V caps are ok.

According to the schematic, there is an Overdrive LED. Is that on? It looks like you need a footswitch to turn the overdrive off. Is there a jack to plug a footswitch into, or is the footswitch perminately attached?

[quartersaw]

The switch cable is soldered to the circuit board. The LED light works fine when you stomp the foot switch