I own a Bogner Uberschall Twin Jet with EL34's (jorg installed them straight from the factory)b and had some issues with it lately that I'd like to consult on with you.
We are recording our first demo now and there's alot of pressure in the studio and I guess that what made me turn the amp on stnadby mode without a speaker load - I've owned a tube amp before and it never happened to me, I feel really bad about it but let's forward with the story.
The amp stayed on standby for around 5 miutes without a speaker load till we realized it and turned it immidaitely off.
We turned the amp on again and there was a sound, but after awhile I started hearing strange noises from the amp itself(not from the cab), 15 minutes later the channel light's flickered and the amp didnt make more sound, it did turn on though, it smelled like something was burned inside.
I took it to a tech, the tech inspected it and said that the fuse was blown and that the power tubes may have got a strong hit and that he's not sure they'll hold on but that I can try using them.
I took the amp home, played through it for 2-3 hours, everything was o.k, but on the studio the day after when we had another recordng session, the amp stopped making sound after around 15-30 minutes
of playing, and this time we verified taht everything was in place. This time there was no flickering, the amp just stopped making sound without anything happening, just like that.
The tech said that if it was on standby without a speaker load than the amp itself couldnt be damaged and it's the power tubes.
I have a set of TAD EL34 BSTR I can install, I just wanted to consult with you guys and ask:
1. Is it really most likely the power tubes that are causing the problem?
2. What is the plate voltage of an EL34 twin jet from the factory?
3. Where is the trim pot placed?
4. Around where should I bias the tubes?
The burning smell is bad, bad juju. Either you lost/started losing caps, or the OT, neither of which is good news. Id start with the tubes and see how it works.
If you pop the chassis out, are there any melted or otherwise defunct looking caps or other bits? Anything ooze out of them or the OT.