[Milsurplus] Power Tube Life Question

[Richard Brunner]

Yes, thoreated filament tubes may be operated at reduced filament
voltage as long as the output and distortion level is acceptable.  Tubes
rated for pulsed operation especially may be operated at reduced voltage
because high peak current is not required in audio and class C operation
as in pulse service.  Acceptable filament voltage level must be
determined by test, and will change with tube life.

Richard, AA1P   


On Tue, 2010-03-16 at 17:43 -0700, J. Forster wrote:
> This relates to the 500 Watt audio power amplifier for the 1MC PA system
> on the Massachusetts again.
> 
> The amp uses 4 type 838 tubes, push-pull and parallel connected, with
> directly heated cathodes (flaments) presumably Thoriated Tungsten,
> although the RCA data sheet does not say specifically.
> 
> Since the tubes are somewhat precious, I'd like to run them at reduced
> filament voltage (maybe 5-10% less) to extend their life. However, I'm
> concerned about loss of Gm and/or emission from prolonged operation with
> the reduced voltage.
> 
> The amp has separate plate and filament transformers, BTW.
> 
> Can anyone provide some guidance, please?
> 
> Thanks,
> 
> -John
> 
> ================
> 
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