AMPEG SVT 3 Pro

[cgates56]

Amp keeps blowing V3, I have replaced it twice with a EH12ax7,

need help, please

[oc disorder]

You could have just been unlucky..
all I can suggest is check the voltages as per the attached schematic
and make sure the 120v is not getting through a leaky C19.
Dangerous voltages inside so be careful let someone know what you are doing .
Does it sound ok when its going ?

[Enzo]

What do you mean by "blowing?"

V3 is just a preamp tube, not under any stress. Shouldn't be much the circuit could do to it. But it is a cathode follower, and in this circuit it has about 120v on the cathode. SO some brands of 12AX7 object to high cathode voltage. Try a different brand.

[cgates56]

Looks like the tube is shorting, the filaments do not light on my tube tester , where a known good one does, I replaced V3 again with a NOS 12AX7 and the amp is up and running again I will just have to run it a few days and see, I have also order a set of JJ's that were in the unit from the factory and will install these, they should be in in a few days.

[cgates56]

Fixed

I replaced all the tubes with JJ's and solved the problem,

thanks for all the help.