On Wed, 27 Oct 2004 12:34:22 EDT TexasRF@aol.com writes:
Hi Gerald,
> I am looking for some advice on adjusting the filament voltage on a
TH347
> tetrode used in my 1296mhz cavity amplifier. The TH347 is a directly
heated
> cathode tube.
<snip>
> Does anyone out there have input on the effect of elevated filament
voltage
> during periods that the cathode is not emmiting? In other words, is
tube life
> compromised during standby periods or is it only for operating periods
that
> matter?
Yes, standby time counts!
> Adding a filament voltage regulator is complicated by the 34 amp
current
> requirement for the tube.
Not necessarily.
One could build a simple primary side regulator using a suitably
heatsinked power FET, as the control element, connected across a diode
bridge placed in series with the filament transformer primary. The gate
of the FET may be driven via an optoisolator from a TL431 connected in a
commonly found secondary sense circuit.
> It would be fairly easy to switch in a small value
> resistor at the filament transformer primary to reduce the
receive/standby
> filament voltage but I wonder if this is a viable solution?
That feature would be an easy addition to an electronic regulator, as
would a soft-start.
This almost sounds like something that Ian should add to his product
line. :-)
> Any comments/suggestions are appreciated.
>
> Thanks/73,
> Gerald/K5GW
You're welcome & 73,
Marv WC6W
*
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