Need help with my JCM900 fast!

[Speedica]

Mjello! I am doing a concert friday, and now my JCM 900 model 2100 is giving me a headache! It starts to fade out some times, I checked the cabels, and it is not them. What is wrong, and how do I solve the problem

[nightfiend14]

I believe when it starts fading it can mean the tubes are wearing out, but I could be wrong, somebody else correct me on this if so

[guitardevil2005]

when ever i have volume probems with a tube amp the first thing i do is check the tubes, but im no pro on this so i cant give a definate answer, how long have the current tubes been in the head?

[carlos grijalva]

Check your amp, i had the same problem, also check the wiring inside the guitar it might've got whirled up.

[Speedica]

It's not my other gear, it's definitely the amp. I bought the amp used, but he said he just changed the tubes, and they look new to me. But maybe he lied to get it sold :P

I checked the wireing, and it's okay... So it's the tubes or what?

[Gresh]

Get new tubes, preamp and power amp. Change them one at a time and test after each change. It might be a tube, it might be a socket. It's most likely a power amp tube issue if it is a tube issue at all, but preamp tubes are cheap so just cover all the bases. Problem solving is process of elimination so it's important to only change one thing at a time, check it, then change something else, check it...and so on.

If you've got a gig, even if you get this "fixed" I'd rent or borrow a backup just in case.

[Ant1981]

Tubes!

[rgr]

It would suck to spend the $ for a full set of tubes and that not be the problem, it's probably worth taking to a tech ASAP, it could be a loose tube socket, bad cap, who knows.

A backup set of tubes is never a bad idea, but no guarantee that it will fix this problem.

[wallopwallop]

Take it to a tech and get it checked out. Just like your car needs to go into the shop for maintenance once in a while, tube amps need the same TLC.

You can buy new tubes and swap them out yourself by all means but the amp will most probably need to be rebiased for the new tubes slightly to get the amp sounding tip top. This is definitely a job for a specialist. This link describes the need for proper biasing better than i can:

http://www.watfordvalves.com/pdfs/guitarv10n3p120.pdf

Scroll down to page 3 where there is a whole section on biasing.

Good luck!