Re: MODEL T TC'S (FIRST LIGHT AND FIRST BLOOD)

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

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

Some very preliminary results for a very very crude setup with a small
amount of time invested.

	Threw together a primary (3" dia, # 17 wire about 2" long) today which
could tune with 1000 pf to the frequency of the secondary from my little
TC.  Because of a severe case of bad think I can't adjust the coupling,
a situation I intend to fix "some day".  The coil will tune to about 730
kHz with no top load, and to 675 kHz with a small semi-toroid.  When
running about 30 watts input from a small NST I can get pretty hot 5"
streamers from it.  Anyhow, put that coil in the new primary and fired
up the coil in the "mode that god intended".  Here's what happened.

	First, tuned the primary circuit to about 650 kHz with the secondary
off, frequency estimated from an absorption wave meter.  Then installed
the secondary and realized I had a bad overcoupling problem.  Ran the
coil with about 4.5 watts input (around 0.7 to 0.8 amps at about 5.9
volts) and set the gap so it was just firing smoothly.  Anyhow, with the
secondary that way I observed a classic double-tuned behavior, with
wavemeter showing frequencies of about 575 kHz and 780 kHz.  Under this
condition could get a nice fat 1-1/8" spark between a screwdriver and a
map pin sitting on top of the toroid.  In the dark there was no visible
discharge from the toroid, but about 1/2" brush discharge from the end
of the pin.  More ozone smell (think it really is ozone in this case)
than I expected.  Playing around with opening the gap and wedging a
popsicle stick into the vibrator could get pretty hot 1-1/2" streamers
when the primary current was about 1.5 amps.  Next experiment was to
separate the primary and secondary, thus operating the thing in a
"magnifier" mode.  A bit over 1" sparks sparks.

	Bottom line is that in this condition the thing works about as well as
I can ever remember getting a slightly better setup in about 1940/41. 
That coil had a much longer primary, smaller in diameter, and the top
terminal was a needle stuck into a block of wood.  In retrospect I'm
sure I never got the thing tuned, as when I used a 4500 volt NST I never
got over a couple of inches, but thrilled with that!

	Before I quit playing with this setup I intend to make the coupling
adjustable, try to get better tuning, then run the coil on both 6 and 12
volts and report the results.  Nothing at all spectacular, I'm sure, but
a bit different project. If I get really ambitious I'll make a higher
inductance primary to work with 500 pfd and compare the results, then
pull turns off the original primary and go to 2000 pfd and see what
happens.  

	Note that I got very much better results running an Exel coil from 12
volts with a transistor driver.  At about 20 watts input could get nice
4" streamers (different coil) and a very nice "crown of fire" around the
toroid in the dark.

	Bottom line to all of this is that you can get some results with the
Model T coil, and that probably it won't drive a very big primary
capacitor.

More later if the ambition strikes me.

Ed