Tom says:
>One should NEVER *under any circumstance* reduce the filament
>voltage of a indirectly heated tube below the tube or equipment
>manufacturer's minimum recommended operating voltage. Any
>reduction below that point in a metal-oxide cathode tube can
>"poison" the cathode and permanently damage the tube.
Is this strictly true IF (and it's a big IF) the emission demands are such that
the emission is still space charge limited? I'm thinking here of some equipment
I've seen where admittedly receiving tubes were run at low (5.5 instead of 6.3)
volts, with low plate and screen voltages and currents. These oscillators didn't
seem to have a life problem, but were running under space charge emission
limited conditions.
Not applicable where high peak currents are needed, of course.
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|