22-09-2021, 03:48 PM
(22-09-2021, 02:18 PM)Mike Watterson Wrote: But the issue is magnified by the rod pentodes because when Ia= max, the Ig2 is nearly zero, uA anyway, but at Ia nearly zero the Ig2 is maybe a 1mA. Thus ONLY a series resistor to 80V HT varies Vg2 too much.
That's interesting, Mike.
I've certainly found that Ig2 is low with rod pentodes. What I don't have data for, is how constant, between samples, is Ig2 as a fraction of Ia.
Ia being nearly zero brings Ig2 up to a maximum surprises me - again, for a given valve, I've found the ratio to be constant. The only circumstances where Ia falls and Ig2 rises, is if anode voltage drops to a low level (below the pentode 'knee') - or if the suppressor voltage is made very negative so that electrons are repelled back to g2 and can't make it to the anode.
