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Re: OLD Tubes/Coils - filament power (fwd)
---------- Forwarded message ----------
Date: Mon, 3 Mar 1997 11:16:42 -0500 (EST)
From: FutureT-at-aol-dot-com
To: tesla-at-pupman-dot-com
Subject: Re: OLD Tubes/Coils - filament power (fwd)
>> snip
> > *Never* operate tubes (at least those with thoriated heaters) with
> >less than their rated voltages and currents. Doing so will strip the
> >cathodes in short order. You may get lots of filament life with near
> >zero emission. Standard incandescent Light bulbs are a different story
> snip
> >Malcolm
> I was wondering if anyone knew if the 803's use a thoriated filament? I
> am using two 803's in parallel, with several turns on top of the primary
> of the microwave transformer to get about 9.5 volts to power the
> filaments, since this arangement isn't curent limited, am I in danger of
> damaging these filaments?
> Thanks,
> David Trimmell
>>
David,
The 803's do have thoriated filaments, and the tube manual suggests keeping
them within 5% of their rated voltage, so your set-up should be OK. But it
would be nice to add another turn or so to the transformer to raise the
voltage to 10 volts, since at full TC power, the voltage may drop a little,
depending on the transformer, etc. Current limiting is not required for the
filament supply, since when the voltage is correct, the current will be
correct, based on the hot filament resistance.
Happy tube coiling,
John Freau