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Re: OLD Tubes/Coils - filament power



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aaah, this sounds REALLY dangerous.  I don't know what circuit you will use 
this in, but usually the filament must be close to the cathode voltage, and a 
battery charger will not have significant breakdown voltage (beyond UL reqmts 
- e.g. around 200 v) between the pri and secondary - filament Xformers for HV 
tubes have high values for this insulation and specify the value on the 
xformer - for example, I had one which specified 20,000 V.  If you use the 
battery charger you will at best destroy it or your circuit, and at worst kill 
someone.  

-----Original Message-----
From:	Tesla List 
Sent:	Wednesday, March 05, 1997 9:45 PM
To:	tesla-at-poodle.pupman-dot-com
Subject:	Re: OLD Tubes/Coils - filament power (fwd)

Dr. Resonance wrote:
> 
> To: Tesla tube experimenters
> 
> If you need a cheap and reliable tube filament supply for some of the older
> tubes try a surplus Schaeur battery charger transformer available from Fair
> Radio Sales, Lima, Ohio  Tel. 419-227-6573.  They deliver 12 volts at 10-14
> amperes (you can also parallel some of the secondary windings).  It is very
> easy to remove a few of the heavy outer windings to get the exact voltage
> you need to match the tube you are using.  The good news is the price --
> around $12.00 surplus.  If you are willing to remove some windings they
> also have some oddball voltages around 16 and 20 vac for even less money
> that will deliver 10-15 amps out.
> 
> DR.RESONANCE-at-tesla-at-pupman-dot-com
> 
> ----------
> > From: Tesla List <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: OLD Tubes/Coils - filament power (fwd)
> > Date: Monday,March 03,1997 9:31 PM
> >
> >
> >
> > ---------- 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






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