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DC coil
> Tesla List wrote:
> >
> > Original Poster: "Payne, Will E" <will.e.payne-at-lmco-dot-com>
> >
> > Kip, (not a list subscriber) replies to some comments from the list I
> > forwarded to him about his DC Tesla Coil as presented on
> > http://www.altair-dot-org/tesla.htm
> >
> > <snip>
> >
> > > ----------
> > > From: Kip Turner[SMTP:kip-at-mindspring-dot-com]
> > > Sent: Monday, October 26, 1998 11:19
> > > To: will.e.payne-at-lmco-dot-com
> > > Subject: My tesla coil
> > >
> > > Will,
> > >
> > > I have to present some arguments and reasons for the design of my
> > > Tesla coil.
> > >
> > > We were two high school boys and it was necessary to keep the cost
> > > to approximately zero dollars.
> > >
> > > The 3B24's were available as WWII surplus at a very low price.
> > >
> > > Using a charging choke would have greatly exceeded the voltage rating
> > > on the capacitor we had. And it would offer no advantage, if we
> > > went to a higher voltage, lower capacitance. It would also increase the
> > > time to charge the capacitor if it held more energy. We were near the
> > > capacitor's rating.
> > >
> > > Since this design was using coupled tuned circuit, the total spark
energy
> > > available is related to the stored joules and not the voltage at which
> > > it was stored. The other would be more complicated and more expensive
> > > and provide no gain....unless a capacitor with more energy storage was
> > > available for the higher voltage.
> > >
> > > Standard, high voltage rectifier, filament transformers of this period,
> > > designed for medium power radio transmitter power supplies were readily
> > > available and could operate at this level ( near ther "test" rating ).
> > >
> > >
> > > 73,
> > >
> > > Kip
> > >
Kip,
You _were_ stressing the heck out of your filament transformer! You
just admitted you were using it near it's "test" rating. What you
didn't admit was that such transformers were not subjected to full
system RF power impressed on the DC bias (perhaps 20 kVDC?), they were
designed to take. Bypass capacitors at the RF power tube in a
transmitter application were/are _always_ employed, both to improve
the
efficiency of the circuit, as well as to protect the filament
transformer from this very damaging RF. In a transmitter the rectifier
tubes were/are not subjected to the full RF tank coil output swing of
the system, just a low Hz mains frequency lumpy version, and fractional
at that, of the Supply DC HV output. High voltage RF of at least twice
the average DC cap charging voltage was impressed upon your filament
transformer secondary winding against the core. Such RF is capable of
damaging many insulation systems at much lower than their DC test
rating. I maintain that your design simplicity was in this respect,
chancefull and the results lucky (as are many greatly simplified max
power designs).
The cudo's you already were awarded! : )
Robert W. Stephens