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Re: I did some *real* vttc coiling...

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

Thanks for the update, Brett!  Your progress is
inspiring.  My VTTC parts continue to trickle in.  I
hope to be wiring something up in the next couple of
months (am currently between houses right now, so no
workshop--I'm going bananas!).  I'm banking on a
mid-March hamfest (Seattle-area) to provide a few
parts...if I'm lucky, maybe some big mica transmitting

Aaron, N7OE

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: Brett Miller <brmtesla2@xxxxxxxxx>
> Fellow VTTC coilers,
> Well, since I have been waiting for certain parts to
> arrive in the mail for the 833A project, and also,
> waiting for the hamfest, I have been seriously
> anxious
> for some actual vttc experience.  After coiling for
> nearly a decade, I realize that it can be foolish to
> get eager and force things to run with substandard
> components and ones with incorrect specs.  However,
> yesterday I started thinking about all the old
> triodes
> I have collected in the closet, and how many little
> mica caps I have sitting around.  I also have a
> small
> Zebra TAN-100TT MOT which still has its shunts.
> So I decided to whip up something in a few hours
> from
> my junk box and see if I could at least get it to
> oscillate.  I based this attempt on a single 3c24 (I
> have 4 of them in boxes) triode.  The datasheet
> looked
> promising...plate voltage = 2000 volts.  An hour or
> so
> later I had a 3.5" diameter primary/feedback over a
> 1.5" secondary (only about 2 inches long) which I
> had
> wound a few years ago to demonstrate a crystal radio
> to someone.
> Well, I got an e-field that could light up a neon
> lamp
> from a few inches, as well as a small flourescent
> bug
> light, with very little sparks to speak of.
> Obviously
> I needed heavier jumpers, especially for the
> filament
> and tank circuit...and it was *way* out of tune, but
> I
> familiarized myself with the Class C Armstrong and
> gained some confidence for my upcoming 833A coil.  I
> eventually cooked the plate on one 3c24.  Another
> look
> at the datasheet showed a low current rating.  Raw
> AC
> and no staccato - bad idea.
> It was a lot more fun for me than it looks:
> Later I substituted the primary and secondary for
> the
> ones which were built for my 833A system.  About 1
> inch sparks...still out of tune and I had not
> installed primary taps yet.  Then I substituted the
> 3c24 for my 304tl.  Plate ran much cooler, 3 inch
> sparks but still way out of tune.  With the 304tl
> the
> skinny jumpers to the filament transformer started
> smoking.  I won't be using anything smaller than
> awg10
> or 12 in my 833A coil, not even temporarily.  One
> thing I learned here is that you can't mess around
> and
> jumper things together with tube coils and expect
> even
> mediocre results.  I was able to experience the
> consequences of higher RMS currents first hand in
> these experiments.
> I had a taste of VTTC action, I have now
> disassembled
> that lashup and am focusing on nearing the
> completion
> of my 833A coil.  I have a 28 turn primary with a
> tap
> (added last night) on turn 20.  I will probably add
> several more, possibly placing a tap on every turn
> from around 18 to 28, something like what Cameron
> Prince has on his primary.  John Freau has
> imphasized
> how tuning, impedance matching, and overall
> efficiency
> are hard to predict and model on a vttc.  I now have
> personal experience with this dilema working with my
> own coils.  This looks to be potential for a lot of
> fun in the future.
> Today I received an RCA 833A socket for the filament
> pins.  You can look at a photo of it here:
> It looks a lot like Cameron's, but I believe his is
> a
> bit more convenient to mount.  Nevertheless I have a
> few ideas for this one.
> -Brett
> Bored stiff? Loosen up...
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