Amp Issue

[Trussrod]

I replaced a 12ax7 the other day and that fixed the lost gain issue I had. The next day the problem was back so I replaced a second tube and the problem was solved again but only for a few hours. Does anyone know what the problem might be? I don’t want to replace pre-amp tubes everyday. The amp is a JCM2000.

I have a multimeter, Weller soldering station and can borrow a capacitance meter if necessary. I know how to test diodes, resistors and other components, etc. I figure Twitch, Cygnus and a few others can help here.

TIA

[Cygnus X1]

Cleaneth thy sockets.

[Twitch]

Just had a similiar prob with my X100 yesterday when I swapped some preamp tubes around. I agree w/ Cyg, clean the sockets. The easiest and cheapest way to do that is find an old dead tube and put it in and out of the socket numerous times, even better you could put contact cleaner on the pins and do it. Also, make sure the tubes pins are correctly aligned with the socket. They will go in wrong if youre not careful(but miraculously they will indeed function this way sometimes but theyll fade in and out or cause other problems). If inserting them blindly, a way to know theyre in correctly is to try to rock them, if they dont rock or rock veeeeeery minimally then you should be good. Also when pulling an old tube out, pay attention to where the gap between pin 1 and 9 was in relation to something and that should also give you a hint as to the orientation of the tube socket for proper insertion. Hope this helps.

P.S. The tubes should fit very tightly in the socket, if they dont then youll need to retention the contacts of the socket which can be done with a simple dental pick.

Keep in contact about this. If this doesnt solve the problem then before we say its the amp we may want to look at other pieces of your rig for issues. Dying volume pots and output jacks in your guitar and other pieces of your rig can cause this same symptom.

[Trussrod]

Thanks Cygnus.

Thanks Twitch. I appreciate your response and did what you said with an old tube and contact cleaner. It turns out my input cable is partially shorting out and killing the tone. It's a straight jack that does not do well having the cable hang at a 90 degree angle--it takes a few days to settle in and cause the tone loss. Thanks again, Twitch, I really appreciate your help and follow-up here--and certainly hope this is the end of this issue.

Another thing I noticed is the loss of bass response after swapping in two Peavey-branded 12AX7's for two of the ECC83's that came with my JCM2000. I've never known there were tonal differences between tubes, but then I never considered collecting--or even building/modding--amps like some people on this board do. This site is a great resource because of members like you.

[Cygnus X1]

No problem TR...and props to Twitch for a more coherent answer.
After a few years you will start a collection of tubes, whether intended or not.

One 12AX7A might "bark at the moon" in one amp and be just fine in another.
I've even had tubes that will not work in one, but work just fine in another.

Don't toss them out unless they are completely dead

[Trussrod]

No problem TR...and props to Twitch for a more coherent answer.
After a few years you will start a collection of tubes, whether intended or not.

One 12AX7A might "bark at the moon" in one amp and be just fine in another.
I've even had tubes that will not work in one, but work just fine in another.

Don't toss them out unless they are completely dead

Good advice. I'll hang onto my old tubes.

[Grim]

Compressed air is the easiest way to clean tube sockets.

Just be easy with it and do it in a garage or something.

Also good for getting the steel wool off that SOMEHOW gets on the pickups despite your taping of them prior to cleaning the fretboard.

[Twitch]

No prob mang, any time. Grim, air will clean sockets of dust but not oxidation and corrosion on the contacts which is the real tone killer.

[Grim]

I noticed after I posted... lol

Good tip about the contact cleaner though, thanks!