Smoked EL34

[panhead]

I just got back one of my SE EL34 amps I built a couple of years ago. The owner said he was A/B -ing it with his other amp (that I also built) during soundcheck and it smoked and he saw sparks around a tube.

The EL34 base is burned between pins 3 and 4 (plate and grid) and the socket it toasted between those pins. I haven't had a chance to look forther into it yet. BTW, the 2A mains fuse appears to be good. Excessive voltage between the pins? Any ideas?

Thanks

Panhead

[PRR]

> he was A/B -ing it

Did it get un-loaded while taking big signal?

[LooseChange]

That would do it.  I've seen more than one Marshall loaded with EL34's with burnt sockets between 3 and 4.

[panhead]

I don't know. I've made clear that he can never run the amp unloaded. I assume he was switching the guitar signal between amps, because this head has its own cabinet and his other amp is a combo. In any case, I think I'll find a lot of damage. Hopefully not to the PT.

[bluesbear]

Maybe not. I've bought a couple of amps (a Marshall and a Musicman) real cheap because an EL34 arced internally and smoked the socket. I just replaced the socket and tubes and all was fine. I used the Marshall JCM800 for years with no problems. My son still has the Musicman (bass head) in his basement for band practice.
Hopefully, you'll find the same.
Dave

[panhead]

The EL34 was a JJ. In my experience so far they have been fairly rugged, but I suppose they can short internally like anyone else's brand. How common is this? I haven't yet had a chance to open the amp up and survey the damage.