[marcoamf]

Hi!
I have built the tester and I was able to correctly test 12AX7s (dual triode).
However, all tests with power tubes (tetrodes and pentodes) presented weird results that I'm questioning (especially because some of these tubes are being used in amps with no problems at all; no identifiable noise, pops or anything).
None of them present any shorts.
When in test mode, plate current and transconductance numbers increase gradually (but faster than when measuring triodes) up to around spec numbers and then grow faster. Current stays quite unstable, varying between 1.5x to 3x spec plate current.
Transconductance also gets unstable, varying from 5x to 10x spec transconductance.
Tubes warm up really fast and I can assume they're hotter than they should (no red plating, though. I didn't wait too long, however, hoping I don't blow these working tubes).
All of them fail GAS test (numbers very different from zero). In most cases, display shows 1 (above meter range).
I have tested 4 different (but old) EL84s. These are quite old, so I expected something wrong, but more on the low current/transconductance side, even though I use two of them in an amp.
2 different KT77s. JJs, were working fine until about 5 years ago.
1 6L6gc (JJ).

A friend had tested my tester and said it was working fine.
Would anyone have a guess about what could have happened and what kind of issue I should try to look for to troubleshoot? (and how to check)

I would guess it's something related to the screen part of the circuit (since 12ax7s are testing fine), maybe a zener that is not limiting what it should limit...

any help is much appreciated.
Thank you!