My amp is boned. Help plz

[gutterking]

This might be too long, but I'm hoping that if I go through everything I've done with it, there might be some information to help you guys help me.

 

I got myself a Red Bear MK120 on craigslist about 4 months ago for $300, but the seller mentioned in the ad that it had two bad power tubes. When it arrived I didn't have a cab to test it with so it took a bit before I ever got it plugged in. In that time I ordered a new set of power tubes and replaced a fuse that I noticed was blown when it got it here and I decided to poke around. With the new fuse I tested it on my friend's cab with the two power tubes it had when I got it (I did make sure to compensate for the impedance difference). No sound except for a hiss that didn't change in volume when I adjusted the volume knobs. I waited for the new tubes to get here, then tried again. Same thing. I decided to swap in his pre-amp tubes to see if anything changed. This time I got some guitar through to the speaker but very faint and clean. When I put it on standby for a bit, then took it off it would increase in loudness notably but still not a decent volume for a couple seconds, then pretty quickly go back to very faint. This is with the master volume and pre-amp volume dimed or very near it. Seeing as his pre-amp tubes were starting to go when I swapped them in, I decided to order a new set, though it took me awhile to get around to it (until about a week ago).

 

I swapped those new pre-amp tubes in today and plugged it into my new old Peavey cab, and the story is pretty much the same, with just a hint more volume.

I did make the mistake of ordering the original Russian equivalent power tubes, which were the same type it was sold to me with, and it hasn't been biased, so I guess that could be a potential problem.

Another thing I noticed is that with the master volume on 0 it still plays, but at a very low volume and slowly tapers from very faint to not quite as faint all the way from 0-10. Also, as I turn the treble knob down, I seem to get a slight increase in volume, and what I'm hearing as a slight increase in treble. Seems kinda strange to me.

 

I'm also wondering if the issues I'm having could have anything to do with the fact that Red Bears were made to use a different type of pre-amp tube. Since it was shipped with 12ax7's, I assume that the conversion was done, but I'm not really sure how to verify that.

 

Should I:

a. Order a matched set of more familiar power tubes and have it biased

b. Take it to a tech and tell him what's going on

c. Pawn the amp off on someone else

d. Search the internetz for bad advice and poke around myself (this doubles as a suicide attempt)

e. Something else

[gutterking]

No one can help me out on this?

[carryonplease]

Sounds like it needs a good lookover by an amp tech. if you take some pictures of the guts i can tell you if the preamp conversion was done, but I don't think that is necessarily the problem. If you have anyway to like test the transformer taps or something like that to verify that they are ok, or just like look inside and see if anything seems out of the ordinary?

 

good luck though i hope you get it working!

[exafro]

The Red Bears aren't wired to take 12AX7's. You need to mod the amp to run them properly, maybe that is your problem?

[carryonplease]

yea he is saying since it came with 12ax7's the conversion was probably done.

[guitarbilly74]

option b

[gutterking]

option b

 

 

Yeah, this is definitely my next move before I do any extra damage to the thing.

My dad and I did peek inside the chassis for a bit and weren't able to find anything that looked out of the ordinary, but I don't have a clue what to look for.

I was hoping someone could help me narrow down the possible problems though.