#1
Hello. I was playing my guitar plugged in a little while ago, and I noticed that my gain knob on my Ultra channel (Peavey JSX) doesn't change anything. I turn the gain on the crunch channel up, and the gain amount increases on the Ultra channel, then I turn the gain up on the ultra channel, and nothing changes. If I turn the gain off completely on both the crunch and unltra channel, there is obviously no gain. If i turn the gain up on the ultra channel, there is still no gain, so i turn it abck down, and turn the crunch gain back up, and there is plenty of gain. If it's any conselation, it's a the 212 combo set to 14ohm, and low output.

Does anyone know why it is doing this? Any help is greatly appreciated.
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#3
Yes. And that's all covered. The switch is on Ultral, and the Crunch gain is supposed to flow into the Ultra gain (or so I understand), it's just the Ultra gain dial doesnt do anything.
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#4
Ok, I really need some help with this...would it be a blown tube or fuse? because recently I shorted out my room, a spare string out of the package fell off of my dresser and the end went into the outlet, sent off a spark, and tripped the breaker for my room recepticles. Would this have anything to do with the amp, even though it was about 3 outlets away from where the amp was plugged in?

Thanks for any help.
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#5
Are all the wires connected? If you can open the back then you should check. If you can't find anything wrong with it take it to a place that could figure out what's wrong, and repair it. Also, there's that one guitarist that quit your band who was good right? Check with him if he knows anything about this kind of stuff.

Man there's a lot of problems with this amp, haha.
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#6
check your tubes. then try changing the ohms that its at. see if it works at 8ohms or whatever. if u cant figure it out bring it to a guitar shop.
#7
I'm pretty sure it's not the tubes, from what I cant tell anyways. I dont want to take the back cover off to check for any loose wires though, because everything is asociated into that panel, and I don't want to mess it up any more that I have to.

There's also not very many good repair guys here, I've heard stories that people send it to get fixed, and they screw something else up and send it back. So, I'unno..
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#8
*bump*

This will be my last bumpage of this thread though, dont worry. I'm going to phone the salesman that sold me the amp, since he said if there were any problems, to let him know, so hopefully he'll have a suggestion or two.
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#9
sounds like a bad pre tube in the ultra channel, at least I've seen amps do that when they have the cascading gain on the lead channel. My friends Krank was doing the same thing, pulled it apart, and one of the preamp tubes had actually fallen completely out of the socket, lol. Preamp tubes aren't expensive, and it's very unlikely that more than one went at the same time. I would grab a couple, so you have a spare, and start swapping in your good tube. I don't know your amp, but the preamp tubes are usually set in a line. The first tube(V1) is usually the input tube, and the last one(V5) is usually the driver, so I would start swapping your the new tube into the positions between the first tube and last tube until you find the bad one(if this is the case). If it's not the preamp tube, it's still a good idea to have a couple spare "known good" preamp tubes.
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#10
Ok, thanks Erock. Now, I'm knew to tube amps, and where abouts would I find the preamp tubes? And how would I know if it's bad? Also, what tubes would be good for a JSX combo?

There are 4 tubes in the back, protected by a steel cage type barrier, and after the 4th (furthest to the right), there's a short silver cylinder, what do you think that would be?

Thanks again.

I'll try to find a picture of the back of the JSX as well, to help you.


Edit: Here's a picture of the silver cylider I was tlaking about.

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Last edited by greendayguitar at Sep 12, 2006,
#11
The preamp tubes will be the smaller tubes, and if there is a metal sleeve, there is probably one inside. I was thinking since you have it isolated to the Ultra channel, it's related there, but I could be completely wrong, I don't know your amp at all. Preamp tubes are cheap though, and like I said, and they are good to have spares of. Really, there are so many different brands of tubes, it's a whole other decision. I like JJ, but there are pleny of others. They are like $8.00 for the regular 12AX7 tubes which your amp takes. It takes 4, but you probably don't need to replace all of them unless you want to. www.thetubestore.com, www.eurotubes.com, and Dougs tubes are some vendors that I've used or heard good things about. How old are your tubes by the way, power and pre?
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#12
I have no idea, I've had the amp only about a month, so Im assuming they are the stock tubes, which came with the amp to the store.
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#13
ic, well the rest are probably fine then. I would just pick up a couple 12AX7 preamp tubes from one of the vendors I listed, or a local shop if they carry them. It's a cheap way to troubleshoot it yourself, and you won't waste anything by having a couple spare preamp tubes. IMO, it's going to be one of the tubes between the first tube last tube. The jacket probably has the input tube, since any noise there would get amplified thru the chain. I think I've seen them on driver tubes too though. Those would affect all your channels though, not just the ultra. One is probably going to be for reverb, since the combo has 1 more tube than the head, and includes reverb. So, I'm guessing one of the 2 middle tubes.

BTW, the tubes pull straight out and go in the same way, they don't twist. They are on pins, that fit into a socket. You can rock them slightly when you take them out or put them in if they are stubborn, but keep in mind they are on straight pins. There will be a larger gap in the pins at pin 1, and this coressesponds to a gap in the socket so you can align the tubes correctly.

edit 2: Make sure you look closely at what tubes you are dealing with also. Your amp has 4 power tubes, and 4 preamp tubes. The preamp tubes will be tiny in comparison to the power tubes. Your powertubes will probably say EL34 somewhere on them, and your preamp tubes will say 12AX7 somwhere on them.
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Last edited by Erock503 at Sep 12, 2006,
#14
In that picture it says you can switch it from EL34's or 6L6 GC's, i have this amp and was wondering what this does. This maybe a stupid question but do you need 6L6 tubes to use that switch or what?
#15
that means it adjusts it's bias to run EL34 or 6L6 tubes, they are different types of tubes. They are slightly different in the tone they produce when they are amplifying your sound. For example, most Marshall use EL34, while Fender and Mesa use 6L6, for the most part. This doesn't mean you can swap them in different amps and sound like the other, but they both have certain characteristics to their sound. Eurotubes has a pretty good description of the differences, at least with JJ's, but it should relate to others too. http://www.eurotubes.com/euro-e.htm. You would want 6L6 tubes if you were using the 6L6 setting, yes.
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Last edited by Erock503 at Sep 12, 2006,
#16
Wow, this is confusing lol. I can only see 4 tubes in the back of my amp, and they're rather large, does this mean that my preamps are covered by something?
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#17
There are going to be 3 preamps tubes near eachother, and one preamp tube closest to the 4 power tubes, which is the driver. The preamp tubes might be covered by metal sleeves like in your pic. That one in your pic looks like the driver tube to me, since it's so close to the power tubes. That's a guess though.
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#18
Well, if that oine is the driver tube, how come there are no mroe tubes around it except the 4 power tubes? Im sorry if I'm frustrating you, im just confused with tube amps ATM.
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#19
?

Most amps have a few 9 pin preamp tubes, and another 9 pin phase inverter. Then you have some powertubes, either octal(big socket) or more larger 9 pins.
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