27-10-2023, 11:20 PM
Well...
It could be that at 0.7V the filament is much more an equipotential cathode, so the electron beam is more uniform (not near cutoff at one end, and at verge of grid current at the other.
But it could instead be temperature related... discussing with a friend she pointed out that older, bright-emitter valves frequently had a filament rheostat to enable a 'sweet spot' to be found.
And also, that some low-level valves (indirectly heated) were operated with slightly reduced heater power, allegedly for better performance.
Which, if any, is right? It's going to be time for a play, I can see...
It could be that at 0.7V the filament is much more an equipotential cathode, so the electron beam is more uniform (not near cutoff at one end, and at verge of grid current at the other.
But it could instead be temperature related... discussing with a friend she pointed out that older, bright-emitter valves frequently had a filament rheostat to enable a 'sweet spot' to be found.
And also, that some low-level valves (indirectly heated) were operated with slightly reduced heater power, allegedly for better performance.
Which, if any, is right? It's going to be time for a play, I can see...
