Valve amp troubles

OnTheRopes

A little while back I posted on here about my hissing Kustom 72 Coupe, anyway I took it to a tech who located the fault as the pre amp valve (12AX7).
It has been sound since then but the problem has started again only this time even noisier. I have ordered another valve but wondering if this is a bigger problem? Any thought?

ICBM

If it is the same valve that’s gone again, chances are it’s more than a coincidence. The likely cause would be a shorted cathode cap, which would make the valve run extremely hot and kill it quickly.

OnTheRopes

Do you reckon I should replace the valve and see how it goes again before taking it back to the tech. (A pain as its a long way) or just take it straight there?

ICBM

I would take it straight there - although call him first, he may be willing to post a valve out to you to try, it would save you both the trouble.

It’s not totally impossible it’s just a coincidence, although very unlikely for two valves to fail in the same way like that unless there’s another cause.

DJH83004

Do you actually know which 12AX7 he swapped out? there are a group of three together, 2 x preamp, 1 x effects loop and the one grouped with the output valves is the PI. As you have already ordered a valve I would temporarily swap it for the one he changed to see if it cures the noise, then give your tech a ring to discuss next steps.      

OnTheRopes

Thanks both, I will give him a call

DJH83004

Not sure where your tech is based, but if it is more convenient I am in North Notts, would be happy to check it out if needed. 

OnTheRopes

DJH83004 said:

Not sure where your tech is based, but if it is more convenient I am in North Notts, would be happy to check it out if needed. 

Might be do-able I'm between Buxton and Bakewell and current tech is based on the outskirts of Manchester/Glossop. I do work in Chesterfield from time to time so may be able to drop over that way.

DJH83004

Entirely your call, Chesterfield is a pretty straightforward run over to mine, no issues either way. Cheers, Dave

OnTheRopes

The valve arrived today so i tried it first in the PI. Seems to have done the trick (for now at least)

DJH83004

Good news!
to be honest the phase invertor is worked quite hard particularly driving 4 x 6L6s, my choice in that position would be a JJ as they tend to be more rugged and don't affect the tone that much as a PI, but not sure what the tech fitted or what you replaced it with mind.  

OnTheRopes

DJH83004 said:

Good news!
to be honest the phase invertor is worked quite hard particularly driving 4 x 6L6s, my choice in that position would be a JJ as they tend to be more rugged and don't affect the tone that much as a PI, but not sure what the tech fitted or what you replaced it with mind.  

Cheers
I replaced a 12AX7EH with the same. Not sure what are in the Preamp and FX Loop or which he changed but Im sure he said the Preamp and gave me the old one so I could re-order if required.