Red plating tube questions

moltenmetalburn

Active member
Went to play diezel einstein amp and heard weird cracklings.

I narrowed it down to single red plating JJ KT 77.

Can I just assume it was the tube as Ive played this amp without a single issue for a year on these particular used tubes which have an unknown lifespan.

Or do I REALLY need to take it to a tech to have it all looked it.

I was hoping to buy a new quad and bias them up to see what happens but didnt want to risk amplifier damage.

Thanks!
 
Did it blow a fuse? I'm no tech, but had the same thing with a Splawn QR. Blew the slo-blo fuse, replaced the fuse, Replaced tubes with a new quad and it was fine.
 
MetalHeadMike":euge6prx said:
Did it blow a fuse? I'm no tech, but had the same thing with a Splawn QR. Blew the slo-blo fuse, replaced the fuse, Replaced tubes with a new quad and it was fine.

Nope, once I tracked down the noise to the tube (3minutes or so) I shut it down.

Ordered a quad to be delivered Thursday.
 
As tubes age the bias will drift. Seems you caught it just in time before it shorted and potentially took out more components with it.

Swap the whole set with new glass, bias them up, and you should be good to go
 
glpg80":2p7v26oi said:
As tubes age the bias will drift. Seems you caught it just in time before it shorted and potentially took out more components with it.

Swap the whole set with new glass, bias them up, and you should be good to go

Yup, you're probably good to go with new glass. Just make sure to check and set the bias.

However, when power tubes go funky on me like this, I pull the chassis and have a look at the screen grid resistors.
Make sure nothing looks burnt, and if you can, check them with a meter ( amp off and unplugged of course!! )
They should all read approx. the same ohms, in this case probably 1k. ( sorry, not intimately familiar with the circuit ).
Make sure they aren't shorted or open.
I searched for a gut shot of an einstein, and it looks like the 4 circled resistors are the screen grids. Diezel support could confirm.

If everything looks good, then pop the new glass in, bias them up, and rock out.
If there is anything strange with the screen resistors, take it to a tech and DO NOT use the amp until the resistors are replaced.

The chances that there are any issues is small, but it never hurts to check....

Good luck with the amp!!
 

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Turned out here were some loose socket pins.

I tightened all of them biased up a new quad of kt77 to 70ma, a bit hotter than my typical 65ma and the amp sounds and plays better than ever.

Thanks for all the help.
 
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