Re: Filament voltages

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Gregory Hunter by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>
> 
> Your filament transformer should develop 10vac
> open-circuit. For example a 120V:10V transformer would
> be just fine. Yes, the voltage will drop a bit under
> load, but 10A across the filament is the important
> part. BTW, I used an old MOT to make a filament xfmer
> for an 833A. I used a hacksaw to remove the secondary
> coil, leaving the 120v primary intact. I wound it with
> 10AWG stranded until I got 10vac output. I think I had
> about 12 turns. I used regular THHN wire and bound it
> in place with cable ties. It can light up an 833A all
> day without even breaking a sweat.
> 
> Cheers,
> 
> Greg

	A note about filament voltage.  If you're driving it pretty hard, the
tube can be damaged more quickly by undervoltage than by overvoltage;
its better to err on the high side, as I doubt if anyone is going to
pile up a thousand hours, or perhaps even 100.  For the 833 and other 
10 V tubes I'd make sure I had at least 10 volts at the tube when the
filament is hot.

Ed