17-10-2016, 08:57 AM
Yes, typical operating characteristics given in manufacturers valve data are with a specific -ve grid bias voltage, the two panel tester's grid voltage is fixed at 0.5 volts -ve which is switched to 0.5 volts +ve when doing the mutual conductance test. the maximum cathode current spec for the EF91 is 15mA.
With 250 volts on the anode and 0.5 volts -ve on the grid the cathode current will have exceeded that limit, even more so when the mutual conductance test is done.
Lawrence.
With 250 volts on the anode and 0.5 volts -ve on the grid the cathode current will have exceeded that limit, even more so when the mutual conductance test is done.
Lawrence.
