[Amps] AC or DC better for indirectly heated cathodes?

[Tom McDermott]

Adam:

	With incandescent bulbs, the lifetime of the bulb is severely
degraded when it is operated off DC due to what is called the 'notching'
effect. This effect is essentially the erosion of the filament metal. To
extend the lifetime of high-current lamps, use of AC is recommended. I'm not
sure how this effect would differ on a tube filament, but suspect that the
lifetime would be degraded if operated DC.

	-- Tom, N5EG



>Are there benefits, advantages, or just risks of using such a scheme? 
> Constant unvarying power at the heaters seems good, but is 'less' 'more'
> to use the cliche.
>
>73 and thanks for any input
>
>Adam