I have used for a month on a HK tube 20.

after one month of a lamp has a default surment lach ...

the level I found them disappointing compared to the groove tube 12AX7 sound is less warm, with highs drier and less bass prsentent ...

it is mainly the lack of heat from my ... So I remi my groove tube.

So for me not photo, enter groove and mesa boogie tube (12AX7 level), the groove tube are much better