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

Last night there was a very loud POP and one of the tube went bright so I moved quickly and turned of the midmonos.

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.

"Bright tube"... RED PLATING?

Does the amp auto bias the power tubes or does the user have to manually adjust the power tube(s) bias?

I wouldn’t take a chance with the JJ e34 power tubes now. If they did Red Plate they more than likely are done for. It is possible circuitry may be damaged in the amp as well. You may need to have a Tech check out the amp.

Example of a Red Plating tube.

https://www.youtube.com/watch?v=6Ecrh5mglZc   

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http://quicksilveraudio.com/wp-content/uploads/2015/08/MidMonoManual.pdf

OUTPUT TUBE BIAS SETTING
Output tube bias should be set immediately when new tubes are put in; then again in 15 minutes;
and periodically the first few times of using the amplifiers. After that the bias should be checked
monthly.
The bias controls are located between the output tubes near the power and output transformers
To adjust the bias you will need a slot-head screwdriver. Adjust by turning clockwise to increase
bias; counterclockwise to decrease bias.

@tonydennison 

Before installing new power power the bias pot(s) should be turned back (turn the bias pot(s) counterclockwise), so as to not over bias the new tubes. Not doing so can damage perfectly good new tubes.

"Output tube bias should be set immediately when new tubes are put in; then again in 15 minutes;"

Did you do this before and after installing the new tubes?

You said you reinstalled the old tubes and the amp works fine. Just a guess the bias setting was still set for the old used tubes. Is that correct?

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

http://www.grandpas-shack.com/parts/datasheets/6000A(Hickok)_manual.pdf

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

Tests:

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.

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