What is the 7586 Nuvistor electron tube bias using a pull up bias resistor?

(A suitable fuse should be used in series with a supply voltage, eg heater supply for safety)


What is the grid bias of the 7586 at 1.2V plate supply, Pleiades bias conditions?


Before connecting heater voltage the grid bias is as expected 1.2V. As soon as 3.9V heater voltage is applied and cathode temperature start to increase the grid bias gradually drops to -88mV. It would have been typically -700mV without the Pleiades pull up resistor. And of course an even more negative bias should the electron tube heater was connected to 6.3V.


So using a 1.8MΩ pull up resistor the grid bias was measured -88mV and 100mV when a 10Ω resistor was connected in series with heaters. This amplifier operates this way too. When a 6MΩ pull up Pleiades bias resistor was used the grid bias was measured -140mV and 15mV when a 10Ω resistor was in series with the heater supply of 3.9V. (A fuse should always be used in series with any voltage supply for safety).


For schematic, more details see yesterday's' post on MD441 U3, MD211 connected to Pleiades V6 7586 Nuvistor.


http://euroelectron.blogspot.com/2018/07/md441-or-md211-to-pleides-v6-with.html