clean sound breaking up

[night0wl]

Hi guys,

A mate of mine has a mesa .22 with EL84's and he said when practising last night, the amp sounded great for a couple of hours then the clean sound started breaking up. Would this be crook valves? If so, are we talking power valves or the 12ax7's?

I haven't had this prob with mine so I can't help him.

Thanks,
Shane

[UnklMickey]

night0wl said:

...Would this be crook valves? ...

i'm not familiar with the "crook" terminology.

is that a typo, or am i just a bit sheltered.

[night0wl]

Sorry unk, aussie slang at work there

Crook = worn/sick/stuffed

[UnklMickey]

well it could be valves, or something else.

valves are easy to test. you should always have a set of good spares anyway. so replace all the valves (mark all the new ones first), and if the problem goes away, then put back the old ones, one at a time until the problem returns. the last one you just put in is the bad tube er, i meant, valve. throw that puppy out. now you need to get a new valve for your set of spares, but you've found the problem.

put in the good spare set, and the problem is still there?

see your local amp doctor. there's a bunch of things it could be that you can't get at without working around high voltage. most likely a coupling cap has begun to fail, (partial shorting) and is messing up the grid bias on the next stage.

grid voltage something you won't even be able to is something you won't even be able to measure properly unless you have a VTVM.

if you're lucky, it's just one of the valves. so start there.

oh, yeah and try plugging in a different speaker. maybe the cone on that one is creasing.

[night0wl]

valves are easy to test. you should always have a set of good spares anyway. so replace all the valves (mark all the new ones first), and if the problem goes away, then put back the old ones, one at a time until the problem returns. the last one you just put in is the bad tube er, i meant, valve. throw that puppy out. now you need to get a new valve for your set of spares, but you've found the problem.

thanks. I'll tell him to try that but I am not sure if he has spare valves. He owns the music shop I am working in at the moment and he did order some but they are on backorder. The closest (decent) place to have an amp looked at is about 2 1/2 hours drive away so I'm pretty sure he'll leave that as a last resort.

oh, yeah and try plugging in a different speaker. maybe the cone on that one is creasing.

I am pretty sure he plugs into a quad box.

Thanks unk,
Shane

[UnklMickey]

night0wl said:

Sorry unk, aussie slang at work there


Crook = worn/sick/stuffed

yeah i didn't get "crook"


okay, i get "worn"

i get "sick"

and i get..........................wait a minute!


i understand "stuffed"

[night0wl]

My mate apparently found out what the prob was with the breaking up....

That model doesn't have any fan cooling, or any cooling for that matter. He stuck a fan behind it and he reckons it doesn't break up now.

Shane

[dinis64]

There is a problem with some of these amps. The link for mod information is raktron.com/studio22/.

You can also do a search at the "Boogie Boards" forum and there discussion on this.

[night0wl]

thanks dinis64, I will check that forum out.