Re: Filament Issue

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 3 Dec 2003, at 17:55, Tesla list wrote:

 > Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net>
 >
 >  > Pure tungsten filaments are not damaged by running at low voltage
 >  and > in spite of their hellish power requirements it's not common to
 >  use them > where tubes are operate space-charge limited.
 >
 > After all, we all have many pure tungsten filament things in our
 > houses, often on phase control dimmers to reduce the voltage
 > substantially below operating spec. Light Bulbs...

Of course light bulbs aren't used for their emissive properties.

 > I suppose one could have some circuit where the low emission, and
 > hence the low current through the tube, would result in some sort of
 > rise in the plate voltage (shunt regulator, where the tube is normally
 > almost all the way on?) that might cause a flashover, but it would be
 > pretty contrived...

Normally? Class C oscillators with a tank in the anode circuit is a
classic case where plate voltages rise well above the supply as are
PP amplifiers.

Malcolm