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RE: Early versions of Tesla's coil
Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
Isn't this an induction coil that operates when the buzzer contacts open not
when the contacts close as with a Tesla coil? It could therefore not operate
in cap discharge fashion. The capacitor would be to protect the buzzer
contacts from the inductive kick (back emf) of the coil and not as a storage
cap as in a Tesla coil.
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, July 03, 2003 10:26 PM
Subject: Re: Early versions of Tesla's coil
Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>"
On 3 Jul 2003, at 18:26, Tesla list wrote:
> Original poster: "RMC by way of Terry Fritz <teslalist-at-qwest-dot-net>"
> Referring to this image:
> We see an image of an early coil of the type designed and built by Tesla
> the earlier part of his career leading up to the end of the 19th century.
> 1) Has anyone seen any better pictures?
I have the book of the lecture/s and I *think* there is a diagram of
the coil in there together with a spark photo.
> 2) Can anyone accurately describe what various components we are looking
> in the picture?
The coil itself is air-cored, the secondary being wound in two
sections with the primary in the centre.
--(ASIDE: Because I was so fascinated by the brush discharges between
the loops of wire coming off the secondary terminals, I built a
similar machine to see the effects. Mine employed a ferrite core and
was a lot less exacting in manufacture. I used plasitc solder reels
for each secondary half and wound them with PVC-covered wire. I also
popped the whole assembly into a plexi container and oil-filled it
(that was when I discovered that silicone rubber didn't go well with
transformer oil - I'd used it to "seal" gaps in the container joints
The primary of the original was activated in cap discharge
fashion using a buzzer type contact arrangement (the front upright
coil). The hot end of each secondary winding is located where the
leads emerge from the secondary (i.e. the effective center-tap
between the two halves is located just beneath the surface insulation
covering the outer turns. Some of this is probably not well
remembered. I will scan what diagrams I have and send it to you off-
list from home (I'm off work next week). Feel free to share them if
BTW, the effects are not unique to this type of machine and
although building it was instructive, I'd never bother doing it again.
I seem to recall it was around this time that Tesla was talking about
1/4 wave secondaries (from a wirelength point of view) and a 1/2 wave
primary (also from a wire length point of view! which he then all but
admitted was not practical).
> 3) Do we know anything about the power supply input required to drive
> type of machine?
> I know this variety of machine was demonstrated at the IEE in London as
> as at various USA events and was an oil-immersed secondary, not
> ground-referenced. I have seen some of the photgraphs in the lecture he
> presebted ("experiments in alternating currents of high potential and
> frequency" is the approximate title) and also seen the impressive brush
> discharge shots. I know nothing about the primary gap or cap or turns or
> secondary or M or resonant frequencies.
> RMC, England