[sdiy] A simple 12AX7 vacuum tube tester schematic..

[jpdesroc at oricom.ca]

In fact all I want to check is the "on test" 12AX7 gain
and compare it to a 'standard, verified, normal' value.
Since the most regular B+ voltage I see in
the musical tube amps I fix is around 300-400VDC
I'd choose 350vdc stable supply.
Then, correct me if I'm wrong but all I need is a
standard triode stage circuit driven with a suitable
1khz stable source then monitoring the plate
swing voltage (that would swing around 2/3 of B+ value) 
rectified and fed to a small solid state meter driver..
Using a "known reference gain" tube I'd
adjust the meter so its needle is around
50% of the meter span (and put a mark there) 
so lower means the on test tube starts to get weak
and upper means the on test tube is GOOD
and maybe better quality than average
if needle get higher.

What do you think?

J-Pierre