problem with peavey xxx

[bloodline357]

ok, here goes. Last week at a gig i noticed that my peavey xxx head was only working on the ultra and clean channels and that it seemed to be losing power. I already had a new set of el34 power tubes so today i installed them, set the bias switch and the thing still only works on ultra and clean. the crunch channel is silent. i looked in the back of the amp and only one tube was glowing(first in line , left to right) and it seemed kinda dim. It still makes sound but even with the master volume cranked it is very quiet. What in the world has gone wrong with this thing? Thanks for any help.

[emperor_black]

wait a min...peavey XXX has a bias switch? Was it something you got installed??

[bloodline357]

no it was on there when i got it, i bought it used from a guy i know here. dont know what year model it is. but there is a switch inside that says 6L6 on one side and EL34 on the other.

[sevser]

All XXXs have a El34/6L6 switch/bias.

I'm just going to say...Sit tight and wait for one of the experts. I have had my XXX for 5 years without any problems and I put it through hell.

I wouldn't even turn it on till you hear from someone who knows...

BTW what are you running for a cab? How many ohms? is it properly matched with the ohm setting on the head?

[emperor_black]

that is not the bias switch. I have owned a Peavey XXX combo and it had that switch too. That switch merely says which power tubes have been selected. A bias is usually in the form of a Pot.

Power tubes are biased "cold" from factory so they will last longer. You can get a tech to bias the power section such that the tubes will run "hotter" and hence you get a better tone. with different brand tubes, you have to keep rebiasing the amp. So, getting a bias pot installed will save you the money you end up paying the tech each time you change brand.

that said, peavey XXX is a fixed bias amp. So, theoretically you dont need to change the bias.

[sevser]

I know...there is a bias pot as well. Says "Bias adjust"

[emperor_black]

kewl!!

[Cleveland Metal]

Well, I'd probably look to the preamp tubes just for the cheapest possible fix that you might be able to do before sending it off.

Different preamp tubes are usually assigned to different channels and sometimes half of a tube is being shared with another channel possibly. If one channel is out, maybe one tube is whack. And if it is losing power in another channel, maybe that corresponding tube is on its way out too. Worth a look, and a swap of preamp tubes. You can do that yourself and see.



Are you saying only one of the power amp tubes are lighting up? Or is it preamp tubes you're talking about?

If it's the power tubes, that sure isn't good. Possibly a tube failed and took out some grid resistors. I'd think it would put them all out, but who knows (except a tech).

Regardless, power amp tubes shouldn't affect different individual channels, unless when it failed, it killed "some" supporting circuitry that powered "some" of the preamp tubes. I just doubt that as it would probably just shut them all down.

Nonetheless, If it isn't the preamp tubes causing the channel issue, then it needs a tech. And it only one of the power tubes is lit, it needs a tech...

[bloodline357]

thanks for the help guys, i sent it to a shop where i buy all my gear they've got a pretty good tech on staff there so hopefully he can fix it. im running a behringer 16 ohm cab that came with the amp when i bought it, not the best but i only paid 750.00 for the whole half stack, lol.