Re: [TCML] VTTC Coupling

[futuret@xxxxxxx]

Dan,

I don't think I've seen you post on this list previously?
But in any case I remember seeing your VTTC work
many years ago on Richard Hull's tapes.  I remember
you used a metal chassis for your coil and at one point
you used (or were planning to use) five of the 811A tubes.
I remember you showed the bushy looking sparks that
were produced at a certain tune point.

John
-----------


-----Original Message-----
From: Dan Elyea <fsiyfr@xxxxxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Sent: Tue, 16 Sep 2008 2:49 pm
Subject: [TCML] VTTC Coupling



There is a really fun thing that can be done with an overcoupled VTTC.  
You
can't take this to really high powers or you'll chance breakout from the
secondary below the top of the winding, but it's fascinating for the
experimentally inclined.  Also, the necessary close physical spacing 
for the
tight coupling raises voltage breakdown issues between windings, and 
that
limits how far you can push the system.



You have to deliberately overcouple the primary and secondary, and 
achieve
the classic double-humped response.   Get the coupling strongly into 
this
mode with two very prominent humps.  Then, with careful adjustment of 
the
primary tuning, you can get the circuit oscillating on two frequencies
simultaneously.  A scope is very helpful for this.  However, the 
appearance
(and sound) of the output discharge changes dramatically when you get 
the
two frequencies going at once, so a scope isn't absolutely necessity. 
The
discharge looks a lot more like multi-forked lightning rather than the
typical VTTC brush.  With a scope, you can see the two frequencies in 
the
waveform.  As you bring up the HV, one frequency kicks in first, and you
have the typical "regular" VTTC discharge appearance and sound.  Going 
up
higher in voltage, the second frequency kicks in (and the first one 
keeps on
running, too).  You can see it happen on the scope, and simultaneously 
see
and hear it in the discharge.



Try it-you'll like it.  It may not be as long of a discharge, but it is 
much
more interesting, in my opinion.  Running paralleled 811As and 
paralleled
MOTs, I got a loud, dramatic discharge.   Very snappy sound in the
discharge.  The main problem I ran into with this was breakdown between 
the
primary and secondary.  Eventually, I resorted to filling the space in
between them with RTV silicone sealant so I could run full power.  (The
physical spacing between windings was a little less than an inch.)
Secondary was wound on a four-inch polystyrene form with #26 enameled 
wire.
About 24 inches or a little more of winding, as I recall.



Dan



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