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Re: TWO STAGE COILS?
Ed Phillips wrote:
> The schematics show the first circuit being driven from either a
> transformer off the AC mains or, alternately, from a DC source with
> series inductance. There is no "induction coil" in the circuit, but two
> coupled spark oscillators.
Ok. I found schematics of the high-power Marconi transmitters in some
old books. The best description is in a book by Fleming, that says
that the system was his idea, and mentions several patents. The
schematic shows: An alternator (G) in series with two inductances (L)
and the primary of a step-up transformer. Keying of the transmitter is
done by bypassing one of the inductances with a switch (S). The
secondary of this transformer is in parallel with a first spark gap,
and in parallel with the gap is a series connection of a capacitor (C1)
and the primary of a first Tesla transformer. The secondary of this
transformer is in parallel with a second gap, and in parallel with
this second gap is a series connection of another capacitor (C2) and
the primary of a second Tesla transformer. The secondary goes to
the antenna and to ground. By Fleming's text, the first part is
exactly a conventional AC-powered Tesla coil with inductive ballast
on the primary of the high-voltage power transformer and resonant
charging of the first primary capacitor. The book shows also, in
the same picture, a schematic with only one Tesla transformer.
The texts don't explain why two Tesla circuits in cascade (or I
didn't see where). Maybe the patents say something.
Other books show the same schematic, but add capacitors (Cg) in series
with both sides of the secondary of the power transformer, as
"guard capacitors" that have the function of avoiding the formation
of a low-frequency arc in the first gap. Interesting idea. Ascii
art drawing:
V
+--------+ +-Cg-+-C1-+ +---+-C2-+ |
| | | | | | | | |
| ) ( o ) ( o ) (
G ) ( ) ( ) (
| ) ( o ) ( o ) (
| | | | | | | | |
+-L-+-L--+ +-Cg-+----+ +---+----+ =
| |
+-S-+
Antonio Carlos M. de Queiroz