> I don't believe its an issue of filamant "failure" or tube returns but one
> of reduced emission life. The addition of a simple rheostat to the power
> tube's filament circuit makes good engineering and economic sense.
>
> -Paul, W9AC
Amen, Paul.
We are prolonging emisson here. An added bonus of a resistor/rheostat
in the primary of the filament transformer is a bit of inrush protection that
is there all the time. In some of Henry's big commercial amps with multi-
tapped filament transformers, a 10 ohm power resistor is inserted in
series with one leg of the filament transformer primary to do just this.
A cheap bit of insurance that I have incorporated into all of my amps.
When the supply of NOS glass tubes is exhausted, spending a few bucks
to protect a sizeable tube investment makes sense, unless one owns
Richardson stock.
(((73)))
Phil, K5PC
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