by flipper <flipper@[EMAIL PROTECTED]
>
Jun 26, 2008 at 04:49 AM
On Thu, 26 Jun 2008 02:24:52 GMT, lisdon@[EMAIL PROTECTED]
wrote:
>Hello again. I'm still working on my tube testing project. I have been
>trying to determine the transconductance of the 6EJ7 tubes I have. Here
is
>my setup: Plate and screen grid at 240 vdc. Heater at 6.3 vdc. Grid 3
>tied to cathode. Control grid at -3 vdc tied to cathode through 10 k
>resistor. Plate current is reading normal and when I vary the grid
voltage
>and devide the change in plate current by the change in control grid
voltage
>and multiply by 10 to the 6, I get the expected transconductance. I have
>done this using the 240 vdc plate curve and the 200 vdc plate curve.
When I
>adjust the control grid voltage from -3 volts towards -2.5 volts the
plate
>current starts running away and the control grid can't be adjusted any
>further. I have to turn the plate supply off to regain control. Using
200
>vdc as the plate voltage and approximately -2.75 volts on the control
grid I
>measure 15 ma and riseing. Is this normal or is this indicative of a
>problem?
> Thanks,
> D. E.
Hard to tell because your description of the test setup is sketchy but
at 240V plate and screen with Ec1 -3V a bogey 6EJ7 would already be at
or over max plate and screen dissipation and increasing Ec1 to -2.5V
would put both almost twice max.
