21-08-2012, 02:10 PM
(This post was last modified: 21-08-2012, 02:21 PM by Radio Fixer.)
I had reason to test some valves today Rob and refreshed myself with what I believe you refering to here. I dont normally bother with the Set mA/V control and the Good / Bad scale that this is used with.
Like you I am happy to just measure Ia and Gm but probably the control and Good / Bad was included to be like testers who give this supposedly simple indication of a valves goodness.
As it says in the Instructions that you now have, back off Ia and switch to the Ma/V position on the Meter Selector switch and set the expected Gm on the mA/V control. Press the mA/V pushbutton and the indication will be either in the Good or the Replace on the meter. I cant see how you can damage the meter ...
But why bother?
Also, it seems to me that the best test of a valves goodness is the emission. How can Gm not be OK if this is so? Gm must relate to the valves geometry and unless this has gone off (unlikely) or was not correct at the time of build (possible) then its unlikely to be low ... higher than spec seems more common.
cheers Gary
Like you I am happy to just measure Ia and Gm but probably the control and Good / Bad was included to be like testers who give this supposedly simple indication of a valves goodness.
As it says in the Instructions that you now have, back off Ia and switch to the Ma/V position on the Meter Selector switch and set the expected Gm on the mA/V control. Press the mA/V pushbutton and the indication will be either in the Good or the Replace on the meter. I cant see how you can damage the meter ...
But why bother?
Also, it seems to me that the best test of a valves goodness is the emission. How can Gm not be OK if this is so? Gm must relate to the valves geometry and unless this has gone off (unlikely) or was not correct at the time of build (possible) then its unlikely to be low ... higher than spec seems more common.
cheers Gary
