Problem with my amp cleans

[EdwardHimself]

Hi guys my peavey ultra tube 112 guitar amp (no not a bass amp but come on are they really that different?) has a big problem with the cleans. Basically no matter how much i turn the gain down, it still distorts if you input the guitar too loud. I know some guitar amps are designed to do this but it never used to have this problem and i like to have an ultra clean sound so i'm imagine it's something to do with the tubes or something like that. The thing is though is i don't want to spend loads on repairs so is it a simple fix or something more difficult?

[Tinman]

I'm sure someone with more knowledge will come along shortly but it certainly sounds valve related to me.

When was last time the valves were changed?

When was it last serviced?

You could try swapping the pre amp valves around to see if it makes any difference.

Pete

[stevebasshead]

Assuming there's nothing wrong with the amp and the distortion you're hearing is part of the amp's design (some aren't designed for ultra clean although valves certainly can do clean) it sounds like you may want to try swapping the preamp valve to me. Check and see if you have a 12AX7/ECC83 in there, if you have you could drop in a 5751 as a direct replacement, these have typically 70% of the gain of a 12AX7. If it still isn't clean enough then there's other low gain valves you could try. It won't cost much either so it's worth a little experimenting. Here's a list of gain values which may help:

12AX7/ECC83 - 100
5751 - 70
12AT7/ECC81/CV4024 - 60
12AY7 - 45
12AV7 - 41
12AU7/ECC82 - 19

[Tinman]

A quick search brought up that it has 4 preamp valves and that they're all 12AX7's.

My thoughts are that if you swap them around you may be able single a duff one out. Having said all that, if you do find a duff pre amp valve then you might as well replace all 4, particularly if it hasn't been re-valved in a while.

Pre amp valves aren't that expensive.

[EdwardHimself]

[quote name='Tinman' post='697229' date='Dec 31 2009, 02:57 PM']A quick search brought up that it has 4 preamp valves and that they're all 12AX7's.

My thoughts are that if you swap them around you may be able single a duff one out. Having said all that, if you do find a duff pre amp valve then you might as well replace all 4, particularly if it hasn't been re-valved in a while.

Pre amp valves aren't that expensive.[/quote]

good idea, yeah i reckon it is probably something wrong with one of the valves in this case. As for it being part of the design, in my original post i already pointed out that it didn't used to do this before so i think there must be some sort of fault although i might consider getting a lower gain tube for the cleans anyway so it's a bit nicer and cleaner in future b/c i do think it's a bit hot.

[umph]

highly doubt preamp valves would've gone more likely the output are on their last legs, does the distortion sound normal?

[EdwardHimself]

[quote name='umph' post='697355' date='Dec 31 2009, 05:23 PM']highly doubt preamp valves would've gone more likely the output are on their last legs, does the distortion sound normal?[/quote]

Well this is the interesting thing because i hooked the preamp out to the computer recording and the distortion still was there. It sounded pretty fizzy like some old fender or something? I dunno.

[Ancient Mariner]

There are a few things that might cause some sort of fizzy distortion, but diagnosing them remotely and through the written medium is *difficult*. You really should take your amp to a tech where it can be checked over properly. By all means try swapping valves around in the preamp, but if you're having to back the gain off much more than normal and still getting it I'd suspect something has happened in the power supply to the preamp.