23-09-2021, 09:45 AM
(22-09-2021, 03:48 PM)Kalee20 Wrote:(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.
And low anode voltage can mean low current.
See how there is a mirror effect?
