Re: [Fwd: Spark gap not firing]

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

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

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Parpp807-at-aol-dot-com>
> 
> Hi Bart,
> Every text and pamphlet in my Tesla collection, including Circular 74, shows
> the TC schematic with the capacitor connected in parallel with the NST. Now,
> it suddenly
> registers that these older schematics do not pertain to an NST. Until now, I
> was unaware of Terry's paper on the subject. Thanks for calling this to my
> flickering attention span.
> There is learning taking place but it is very sloooow.
> 
> Cheers,
> Ralph Zekelman

	Did a little digging through my library and came up with the following:

	First, the ONLY circuit of a spark oscillator I can find in Circular 74
is Figure 168, page 228, which does show the capacitor across the
transformer.  For what it's worth, this is in a chapter devoted to
sources of signals for measurement purposes.

	Going through some other books of that general vintage I find some more
things of interest:

“WIRELESS TELEGRAPHY”
J. Zenneck
McGraw-Hill, New York, August 1915
English translation by A Seelig of German edition of November, 1912
Chapter VII
“TRANSMITTERS OF UNDAMPED OSCILLATIONS”
PP 173-212.
Almost all circuits show the gap across the AC source, sometimes through
inductors of unspecified value and function.

“PRACTICAL WIRELESS TELEGRAPHY”
EE BUCHER
Revised Edition
Wireless Press, New York  1917
Section 107. High Frequency “Choking” Coils
pp 110-112
Discusses use of inductors to protect the secondary of the (power)
transformer from puncture of the insulation and shorts between adjacent
layers.  “These coils consist of a few turns of fine wire in the form of
a spiral, or a single layer on a porcelain, glass, or hard rubber
tube.”  All of his transmitter circuits place the capacitor in parallel
with the coil and the gap in series with the tank inductor.

“ROBINSONS’ MANUAL OF RADIO TELEGRAPHY AND TELEPHONY”
4TH REVISED EDITION
UNITED STATES NAVAL INSTITUTE
ANNAPOLIS,  MD  1918
Figures 40 through 48, page 108, show varius configurations of spark
transmitters.  Figures 40 “DEFOREST SHOEMAKER”,  44 “MASSIE”, and 46
“TELEFUNKEN” show the capacitor across the transformer and the gap in
series with the tank inductor.  The remainder of the figures “FESSENDEN,
“STONE”,  “MARCONI”, AND “SLABY ARCO” show the gap across the
transformer and the capacitor in series with the tank inductor.  No
mention of “choking coils”.  None of the “wiring diagrams” show use of
anything to protect the transformer.

“The Principals Underlying Radio Communication”
RADIO PAMPHLET No. 40
December 10, 1918
Signal Corps, U.S. Army
Washington  1919
Circuits show both gap/capacitor arrangements.  “Choke Coils”, page 276
shows use of “choke coils to prevent the high frequency condenser
discharge from getting into the transformer and puncturing the
insulation”.  It specifically cautions against "opening the gap too
wide" and causing insulation puncture. Also mentions potting of
transformers in “grease melting at about 115 degress”, and use of
magnetic shunt to limit transformer current while the gap is firing.

	It’s interesting to note that the two military publications use the
term “radio”, while other publications of the times usually use
“wireless”.

	Various amateur "Wireless" publications of that period show either
configuration, but the most common shows the capacitor across the
transformer.  QST, Volume III, August 1919 through July 1920 has only a
few circuits for spark transmitters (spark wa"s becoming passe and CW
was the coming thing, powered by tubes "liberated from the military
during WW1); the first shows the gap across the transformer and others
show the gap in series with the tank.  One picture of a Thordarson "1
kw" transmitter (forgot to write down the month and page) shows the HV
transformer connected to the tank capacitor by some unsupported air-core
coils of perhaps 20 turns and 2" diameter.  No words to go with it.

	Bottom line to all of this is that "you pays your money and you takes
your choice".  Guys have been blowing up transformers for a very long
time and some used protection, apparently some used "strong
transformers", and some had lots of disappointments and failures.

Ed