Re: First VTTC light, and a few questions

["Steve Rosenthal" <sdrosen-at-cwia-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

I have a magazine from fall 1963 "Science Experimenter" detailing
construction of a twin 811a Tesla Coil. It is very staightforward. I can
scan the pages and send them to you offlist if your interested.
sdrosen-at-cwia-dot-com


__________________________________________________
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, July 18, 2000 7:02 PM
Subject: First VTTC light, and a few questions


> Original poster: "Grayson B Dietrich" <electrofire-at-juno-dot-com>
>
> Heyas, All!
>
> For just about as long as I've been building spark gap coils, I've wanted
> to build a vacuum tube based coil...  ...and now I finally have a
> functional one!
>
> Following equations in Duane Bylund's "Modern Tesla Coil Design Theory"
> (a book that took me a year[!] of waiting to recieve-very unreliable
> publisher) I wired up a coil with a single 811A triode.
>
> At first it barely gave the tiniest spark, but with quite a lot of
> fiddling, rearrangement, and finally adding metering of  filament
> voltage, plate current, and grid voltage (the meter wired for grid
> current seems to be nonfunctional :p ) It now runs smoothly, apparently
> well within the specs of the tube.
>
> The sparks are only 2" long at the very best, and I've read that an 811A
> coil ought to be able to give twice that....   ....so here are the
> pertinent specs as best I see them, and a request for advice.
>
> (values measured)
> Plate Voltage: 1030VAC
> Current Draw: 120mA (I'd like to draw more, as the plates aren't even a
> dull red yet, but I don't want to reduce the grid leak resistor much
> more... it is already only 3K)
> Grid Voltage: -120VDC
> Filament Voltage: 6.6VAC (the meter reads a rising voltage as i increase
> the variac controlling plate voltage...  ...when the coil was ill-behaved
> it would increase to as much as 10V, now it only reaches 7V...what is
> happening?)
>
>
> Primary: 4" thin wall PVC form, PVC insulated #18 wire, 23turns, tapped
> at 18, windings are 1 7/8" tall.
> Feedback: on same form as primary, Cottenamel insulated #24 wire,
> 19turns, not tapped just wound on and off (excess spirals in solenoidal
> forms to reduce space taken up)
> Secondary: 3.5" dia. thick wall PVC, #28(a guess, worked right with
> WinTesla) enamel insulated wire, 5.75" winding height.
> Terminal: 2.25" aluminum ball with a 1" wood screw attached, pointing
> strait up.
>
> Bottom turn of secondary is even with top turn of primary (gave better
> performance than with more coupling) Feedback winding is 3/4" below
> primary. Originally this was above the primary, and the coil performance
> was terrible, while the metered voltage and current values were all much
> too high.
>
> Grid Leak Resistor: 3K to 4K, on a 20K 25W rheostat.
> Grid Leak Capacitor: 4000pF, 1600VDC PP film/foil (4 1000pF caps in
> parallel)
> Tank Capacitor: 1000pF, 3200VDC PP film/foil (mini MMC, 4 1000pF caps)
>
> Plate voltage is variable, brought up slowly via variac.
> There is no filtering,
>
> and....    ....Oh, yeah. Just how long ought I to let this thing warm up
> before I apply Plate Voltage? the filament gets orange-white in seconds,
> and doesn't appear to get any brighter if I let it sit there for a while.
>
>
> Also, is it acceptable to run an 811A with a dull-red glowing plate, or
> to what extent is such a thing allowed?
>
> Thanks for any input, and I hope to hear from all you tube coil gurus out
> there.
>
> Thanks,
>
> Grayson Dietrich
> http://www.electrophile.8m-dot-com
>
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