#1
I bought a used Peavey JSX combo a few weeks ago. Recently, it started to crackle/hiss, but mostly crackle. It happened once, then it happened again a couple minutes later. And soon it started to happen more and more often. Pretty soon there was almost no time between it happening so i just shut it off.

I'm 99% sure that it's a tube that was going out/ is dead, but i don't know if there's a way to identify if it was a preamp or power tube. I can see the power tubes from the back of the amp, and they all looked to be functioning like normal from what i could tell.
#2
It's a microphonic preamp tube. Buy one or two and swap them out until you find the culprit. It's very likely that it's only one.
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#4
Buy a balanced 12AX7 and try it in all positions until you identify the culprit. It is always good to have one of those on hand just for this purpose.
It could also be a dirty seat. Try cleaning them by spraying some contact cleaner on the valve pins and working it in and out of the socket a few times.
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#5
Ok, but one of the 12AX7's is used as a phase inverter. Does that require a special 12AX7 tube?

And i'm fairly certain that it was just a tube dying out, since it started to hiss and sputter every minute or so, then got so frequent i just had to shut it off. Seems like it was just a tube that was dying off and then died.
#6
Quote by Pac_man0123
Ok, but one of the 12AX7's is used as a phase inverter. Does that require a special 12AX7 tube?

That's why I said to buy a balanced one. It will work in all positions.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#9
Ok.. bumping this thread for a new(ish) problem.

I got a set of JJ 12AX7's today to replace the ones in my JSX, got home, turned on the amp, and it wasn't doing it anymore. I've had it running for about 45 minutes or so.
#10
^ From what I've gathered JSXs are kinda finicky like this

Quote by 311ZOSOVHJH
just try swapping the first preamp tube with the 3rd one (I think on these amps) for starters.

the V1 preamp will be the one closest to the insert jack. V3 will be the 3rd one down.


^ have you done this yet?

I would so you can validate what is wrong. In other words if you start slamming new tubes in there and all the sudden it works fine you won't really know what you did. I hope I don't come across as a jerk, just trying to help.

guide:
http://s545.photobucket.com/albums/hh384/buckethead_311/Amp%20stuff/?action=view&current=Microphonicpreamptube.flv

What tubes did you get exactly.
Last edited by 311ZOSOVHJH at Sep 9, 2010,
#14
sorry....I didn't think you would actually slam anything in ....I just get bored sometimes when explaining things.

i'd probably just do nothing for now until it crops back up again. You can change preamp tubes while the amp is on btw.
#16
^that is an old fallacy

you can touch them all you want. the oil on your skin will burn off. they can get very hot though so let cool. I use thick leather gardening gloves.


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#17
i had this happen on my valveking with terrible crackeling, to the point to where it wasn't playable.

i posted on here, right before the click to complete order, and somebody suggested a bad speaker cable.

all i did was swap cables, and it has been fine for two or three weeks now.

my hypothesis is, is that over time from a straight plug on a speaker cable gets pulled downward for a long period of time by the cable underneath it, which could lead to cable failure. or maybe even pulling on the jack, causes somthing to mess up.

just a thought, since i assumed you pulled the cable out and put it back in or maybe switched.

i was sure on my amp that it wasn't that, and since it would only take a minute, and i did it and saved myself $100 bucks.
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#18
Like i said, all i've done is take it home, plug it in, and play a bit.

Well, that and take off the metal grille/aluminum covers from the tubes.

I'm wondering if maybe one of the tubes was knocked a bit loose at some point, and playing made it worse, and at some point it got knocked back into place? It seems unlikely but i had the amp on for like 3 hours today and was playing for a fair portion of that and i didn't hear anything.
#19
Sadly, there have been several cases of funky things going on with the JSXs. If you search here I'm sure you can find them. I seriously doubt that if a tube came loose that it would wiggle its way back in nice and snug. They are in there pretty good. If I transport an amp the first thing I do is push all the tubes back in tightly. Another thought would be that a solder connection inside the chassis became compromised (they call it cold joint) and needs a fresh connection.

again....not an amp tech :shurg:

maybe this will never happen again, but if does - do the preamp swap like we were saying and note any differences. Keep you new tubes for when you actually need them.