Why does my Peavey Classic 50 keep blowing a valve?

Toast

A few months ago I replaced the Sovtek valves in my Peavey Classic 50 with JJ's. This was after 5 years on the Sovteks with absolutely ZERO problems.

Then after a few weeks one of the JJ 12AX7's blew (it got discoloured and the amp doesn't sound right). It was die 3rd one on from the left when looking at the amp from the rear. I assumed the valve was faulty and replaced it with another JJ. When the new valve came, after only a couple of hours the same valve went again. >☹

While waiting for the new JJ to arrive I put one of the old Sovteks back in and it performed flawlessly for about 3 weeks.

What's up? The Peavey C50 is FIXED BIAS, so I didn't think it was neccesary to have it rebiased on the new valves.

I really like the sound of the JJ's in the amp, but this isn't going to work. What other valves should I try? What are the odds of getting two faulty JJ's in a row (they where from the same supplier)?

Regards
Johan

AlanRatcliffe

Biasing only affects your power valves anyway. Your 12AX7s and other preamp valves don't need biasing.

While there is a good chance it's a bad batch of valves (otherwise I think the Sovtek would also have blown), it would be safest to have your amp checked out to make sure it's in spec before fitting the next JJ.

Pierre-Cronje

Toast wrote: A few months ago I replaced the Sovtek valves in my Peavey Classic 50 with JJ's. This was after 5 years on the Sovteks with absolutely ZERO problems.

Then after a few weeks one of the JJ 12AX7's blew (it got discoloured and the amp doesn't sound right). It was die 3rd one on from the left when looking at the amp from the rear. I assumed the valve was faulty and replaced it with another JJ. When the new valve came, after only a couple of hours the same valve went again. >☹

While waiting for the new JJ to arrive I put one of the old Sovteks back in and it performed flawlessly for about 3 weeks.

What's up? The Peavey C50 is FIXED BIAS, so I didn't think it was neccesary to have it rebiased on the new valves.

I really like the sound of the JJ's in the amp, but this isn't going to work. What other valves should I try? What are the odds of getting two faulty JJ's in a row (they where from the same supplier)?

Regards
Johan

Check the resistor on the cathode and see if still has the same value. Next step if there is a cathode bypass capacitor check that it is not breaking down.(difficult without LCR meter, so repalce it with a new cap.)