2. amps-preamps
  3. 185575-111109

Is this describing a blown tube, or two blow tubes?

I installed a new set of JJ e34’s a few days ago. Last night there was a very loud POP and one of the tube went bright so I moved quickly and turned of the midmonos.

 

After they cooled I inspected the tubes and they seemed fine so I reinstalled them thinking maybe it was some kind of impurity within the tube. I’ve never experienced a blown tube before.

 

The amps ran great this evening until just now, and another POP and bright tube, but it seemed like it was the other tube, but I can’t be sure. This was followed by a low whistle or hum and I turned the amps off again.

 

Is this simply a run of the mill faulty tube? Could two blow in one day, or could the first one POP like that and then continue to work for another day?

 

Since Ive never experienced a tube fail before, could this have anything to do with the Amp, or is it just a bad tube or tubes?

 

Should I worry about putting my old tube back in?

 

Thank you,

 

TD

 

128x128tonydennison
pdspiegel
26 posts
 

The JJ E34L is a variation of the EL34 which is different tube than the "88" (that I assume is a KT88) that you replaced.  Specifically, the pentode EL34 has a suppressor grid 3 on pin 1 which a beam tetrode like KT88 does not have.  An amp can be made to support both types, but if not, the EL34 suppressor grid could be unattached, or worse used as a tie point for another voltage.  I would confirm that your amp is designed for true pentodes like the EL34 family with a suppressor grid 3.

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tonydennison's avatar
tonydennison OP
409 posts
 

@pdspiegel 

 

You raise a very important point, and yes they are designed for several different tubes including the 88's and the 34 family.

 

Thank you

tonydennison's avatar
tonydennison OP
409 posts
 

@jjss49 

Well the only info you need is to know that I asked whether the sounds and lights described were indicitive of a tube blowing. 

Beyond that, I am using Quicksilver MidMonos with manual biasing and I did make the proper adjustments.

 

Thanks

gs5556
1,239 posts
 

From what you describe I would say it's a typical tube failure if you did not have any problems with the old tubes. Unfortunately, tube infant mortality is quite common as tube factories do not have the greatest quality control, which is why the better tube sellers burn in tubes when they're delivered. But sometimes one just slips through the cracks.

Plug in the old tubes and if all is normal, then get another from Tube Depot. Those guys are one of the best and they'll stand by what they sell. 

Also, with push-pull amplifiers a tube tester doesn't offer much practical use. If a power tube can't hold its bias then that is all you need to know to replace the tube.

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