Maintaining a tube amp

Chronos-X

Chronos-X

Chronos-X

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Hello all,

I've just brought home a very cool Marshall Valvestate 8240 amp, with a tube in the pre-amp. I've noticed its not 100% like one of the same I played recently, and I've heard that the valve needs replacing as a matter of mainaintance every so often.

How often should these things be swapped out and is it something you can do yourself? What's involved?

Thanks :)
 
Pre amp tubes in these hybrid amps very rarely need to be changed!

ive been using my vox for a year and it was used for 2 years before that and they havent been changed.
 
Well this range is from 1991 :D And I've just cracked it open to have a peek, the valve says "Marshall ECC 83" on it so it may well be the original one?
 
whilst you're here dmpoole and whilst its on the subject of tubes :p

can different preamp tubes be put into these hybrids do you know? and would it affect the sound if i put a different one in?

its got a 12AX7 tube in it at the moment...
 
SidewinderINC said:
whilst you're here dmpoole and whilst its on the subject of tubes :p
can different preamp tubes be put into these hybrids do you know? and would it affect the sound if i put a different one in?
its got a 12AX7 tube in it at the moment...
Click to expand...

Sorry, I can't help because I know little about tube amps.
All I know is that in the old days we carried spare EL34's with us for our Marshalls and they came in useful now and then.


Chronos-X said:
Can you tell me what I should do please :)
Click to expand...

Google for one and buy one - just in case.

http://www.guitarampkeyboard.com/options.php?id=12020
 
Right, but is it just a case of unplugging the old one and putting the new in it, does it involve soldering, this "biasing" stuff I've heard about??
 
The preamp valves by definition are not power valves so they will not need nearly as much maintenance as the power amp valves - which your amp doesnt have anyway
 
you can unscrew them, and then screw the new ones in. i'm not sure whether you have to do anything after that with pre-amp valves.

with power amp valves you have to do stuff i think... but that might just be for if you want to change them to a different type.
 
in my JCM 800 the 2 power valves (EL34's) are held in via a spring system and they just slot in, the 5 smaller ones (ECC83's) have a metal cap that screws over the valve to hold it in. once thats off you just push it in. they can only go in one way.

gl!
 
I've known a couple of people buy JCM800s not knowing its a single channel amp :D No overdrive to kick! (You can only twiddle the gain knob or use a pedal)
 
^ footswitchable gain is all you need when you've got that amp :p

and the 2210 are 2 channel anyway ;) and ive just eyed one that i might purchase :p
 
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i think they'd be fine. i was eyeing them up too.. my valves are also due a replace. damnit, it will be expensive..

btw my JCM is the 2205, reverb, fx loop, 2 channels ;). tis nice... :cool:
 
SidewinderINC said:
you can unscrew them, and then screw the new ones in. i'm not sure whether you have to do anything after that with pre-amp valves.

with power amp valves you have to do stuff i think... but that might just be for if you want to change them to a different type.
Click to expand...

Eek, no unscrewing!!! ECC83 (12AX7) is a 9 pin valve that just pushes straight into the socket, try unscrewing and you will most likely damage the pins. You shouldn't really need to worry about biasing as you are replacing like for like and any manufacturing differences are going to be negligable. As for the valves themselves there are plenty of brands out there and as you are only replacing one valve perhaps you could buy a couple of different brands and see if you have any preferences, a 12AX7 is only about £8 iirc.
 
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