Bogner Uberschall twin jet Troubleshooting

[Trippled]

Hi,

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?

Thanks,
Daniel.

 

[Death by Uberschall]

No speaker load on Standby is OK because the power tubes don't see Mains voltage until you switch the amp to ON. Sounds like a "run away" or shorting tube under load. Also check the studio's power for proper voltage and grounding.

To answer your questions:

1. Yes. Also check your speaker cab for a blown speaker throwing the ohm load out of whack.
2. Not exactly sure, but you should expect to see 470-530 volts.
3. Inside the amp or accessible through the external bias test points.
4. 70% max dissipation at idle (speaker load present, all volume knobs off). Between 65-70% is where you want to be.

 

[Trippled]

Where is V1 btw?

 

[Death by Uberschall]

Where is V1 btw?

Closest to the guitar input jack.

 

[Trippled]

There's a 4 tubes and tubes rows? which of them? it's abit hard to understand with that kinda description

 

[glip22]

Where is V1 btw?

It's easy to bias this amp because of the external points. I am not being a dick but if you had to ask where the trim pot is and where V1 is, maybe you should have a friend or a tech check it out.

 

[Death by Uberschall]

There's a 4 tubes and tubes rows? which of them? it's abit hard to understand with that kinda description

Not that hard to figure out.

V1: Input tube for both channels, 12ax7

V2: High gain channel, 12ax7

V3: High gain channel, 12ax7

V4: Clean channel 2nd stage one triode only, Twin Jet Semi Clean 2nd and 3rd stage, 12ax7

V5: Loop, 12ax7

V6: Phase Inverter, 12ax7

V7 through V10: Power Tubes,Uberschall EL34, Twin Jet KT88

 

[se7en]

There's a 4 tubes and tubes rows? which of them? it's abit hard to understand with that kinda description

Preamp tubes are the small ones.

 

[Trippled]

LOL the amp wasnt around and for some reason I imagined t like the preamp tubes were on the other side
so it sounded weird LOL

Yeah it's pretty clear now I'd say.

Thanks man!

 

[glip22]

LOL the amp wasnt around and for some reason I imagined t like the preamp tubes were on the other side
so it sounded weird LOL

Yeah it's pretty clear now I'd say.

Thanks man!

I was afraid for you.

 

[Death by Uberschall]

LOL the amp wasnt around and for some reason I imagined t like the preamp tubes were on the other side
so it sounded weird LOL

Yeah it's pretty clear now I'd say.

Thanks man!

I was afraid for you.

I still am.

 

[Trippled]

LOL the amp wasnt around and for some reason I imagined t like the preamp tubes were on the other side
so it sounded weird LOL

Yeah it's pretty clear now I'd say.

Thanks man!

I was afraid for you.

I still am.

Well I just visualized it the opposite way, that was the whole thing,
Anyway I replaced the H.T fuse again and took it to another studio to play loud for an hour and a half, sounded great, no issues.

 

[glip22]

LOL the amp wasnt around and for some reason I imagined t like the preamp tubes were on the other side
so it sounded weird LOL

Yeah it's pretty clear now I'd say.

Thanks man!

I was afraid for you.

I still am.

Well I just visualized it the opposite way, that was the whole thing,
Anyway I replaced the H.T fuse again and took it to another studio to play loud for an hour and a half, sounded great, no issues.

It was just your tubes or tube. Glad you are back up.

 

[Trippled]

Nah, didnt change a tube.