Re: Early versions of Tesla's coil

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

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

Tesla list wrote:
 >
 > Original poster: "John H. Couture by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
 >
 > RMC -
 >
 > I believe the coil in your photo is an induction coil because in this
 > circuit the normally closed buzzer contacts short circuits the capacitor.
 > When the relay coil is energized the contacts open
 > and a current flows from the relay coil thru the Tesla primary and thru the
 > capacitor.
 >
 > Was the diagram you received the one that is shown on page 75 in the book
 > "My Inventions" by Nikola Tesla and edited by Ben Johnson? This photo was
 > shown on the List many years ago. This is a similar coil to the coil you
 > show and is an induction coil. The photo on page 75 shows only the TC
 > primary coil and not the secondary coil.
 >
 >   With a true Tesla coil the energy is built up in the Tesla primary
 > capacitor and when the voltage across the capacitor is high enough the gap
 > "closes" and the capacitor discharges into the Tesla primary coil. This is a
 > dampened sine wave current.
 >
 > I show a similar circuit in my TCC Guide for the 70 KV TC System. This
 > system uses an induction coil (relay) to store the energy and energize the
 > Tesla primary. The relay contacts are normally closed and open when there is
 > enough energy in the relay coil. The current from the coil then flows thru
 > the Tesla primary coil. The capacitor is across the relay coil in this
 > circuit to protect the coil.
 >
 > If you have a different diagram could you post it on the List?
 >
 > John Couture

	The customary "kicker coil" had the primary of the TC in series with a
capacitor; the the combination was connected across the buzzer
contacts.  When they opened the energy stored in the inductance of the
buzzer coil was transferred to the capacitor; when the contacts closed
again the capacitor was discharged through the TC primary. The design of
such a system is described in Curtis. Perfectly reasonable way to go for
low-power applications.  As far as I know all of the "Tesla coil" leak
detector spark coils operate in this way and are probably being built
still.  I have one built by Rogers Electric in 1916 which works this way
and puts out about a 1" spark.

	An almost identical arrangement was also used for low-power spark
transmitters, except that as a rule the resonant frequency of the
secondary was higher.  Used by guys who didn't have AC to operate an HV
transformer.  Transmitters of this type were used by both sides for
communication in the trenches and can be found in any of the old
handbooks of that era; the few examples which have survived are highly
prized by collectors.  A few years ago I saw one at an antique radio
swap meet.  The buy wanted $250 for it and I've always regretted not
buying it.

Ed