• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

ECC99 envelope failure

2021-12-19-ecc99.jpg

This tube only has less than 20 hours. The glass envelope has a very clean separation.
I wonder what would cause that ?
 
Clearly a manufacturing defect, JJ "should" send you another.

Base glass "button" and empty envelope edges are heated red hot with gas burners and joined together .

That joint did not fail, but extreme heating and later cooling creates tensions in glass.

They are relieved by heating the whole tube in an oven and letting it cool slowly;I guess either that was not done or done improperly.

Watch from 3:20 on