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,






yes, I always post things that other's as well as OP might find interesting, and finding out about stuff is fun.

I have hundreds of tubes, two of the GE Orange and Gray Porrtable Cases repair men brought to the home, and a few drawers full, a mix of used and new.

I test all my active tubes bi-annually as a matter of course, test any from my drawers of tubes when needed for me or my friends, test my friends tubes, test tubes I order.

Like an inexpensive sound pressure meter, they do not need to be 'calibrated' to give you 'relative' answers. If two tubes show the same strength on the meter, they are in fact equally strong, a bit more or less irrelevant unless close to bad.

My Hickock was calibrated by the tech who sold it to me. My little Accurate 157 always closely matched the Hickock. When I got the Accurate 257, both 157 and 257 matched, I preferred the smaller one because my first wife got it for my birthday way back when. 257 is quite portable as well.


I also have a set of quicksilver mid mono and have lost a tube before. You described my experience to a t. For what it's worth I was running mine with kt120 for a long time until I decided to try the el34 which as I understand the amps were voiced for. My humble opinion is that JJ stands for junk junk. JJ tubes are the only brand that I have bought that were bad out of the box and I have an audio buddy who's experience has been the same. I run my mid mono with Tung Sol and could not be more pleased. I am not sure what they are getting for those tubes now after the embargo but I seem to remember not paying a lot of money for them. I hope this was helpful.


120's ? wow, I didn't think that was possible with MidMonos, I assume you have a more modern version than mine. I have a simpler bias mechanism than I assume you have.

I generally like to stick to Gold Lion.



Tube testers are not very good for matching tubes, you may be able to weed out a shorted tube though.

I’m not sure vintage tube testers were meant to match tubes. I doubt TV repair techs needed to match tubes as a rule.

I have a Hickok 6000A Mutual Conductance tube tester that I use to test tubes.

User Manual

It doesn’t match tubes per say, example plate current, but it is useful in others ways.


Shorts. (A must) See page 6, manual.

(Quality). Good, marginal, bad, test. (Very useful.)

Gas (Grid Current) Test.

Mutual Conductance Test. (A must for me matching Mutual Conductance of the dual triode sections of a 6922/7308 signal tube.)

Life Test. When a tube tests low good on the meter, or marginal, the life test tells the user how much life is left in the tube or if it should be replaced.


Tube testers don't use real world plate current under load, so the life test doesn't mean much.