RE: VTTC/ would this work?

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

Original poster: "Andy Cleary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <cleara-at-twcny.rr-dot-com>

Hi Steve,

	I'm afraid I'm also new to the VTTC business, but having just
completed my first I figured I'd share a few things that I learned
along the way...

	Firstly, I'd say to follow the schematic as CLOSELY as possible if
you don't know alot about VTTCs(like me)!!  I used David Trimmel's
schematic as you have seen before, but instead of his dual 803's I
used a single 4-125A tube.  I followed his schematic almost exactly,
except for the tube (and the primary/feedback coils as noted below).
All my other components are within the ranges he gave (except as noted
below) and to this date, instead of the 12" discharges the 4-125A is
capable of I have gotten no more than 1" :(  I figured I'd be able to
tune it up using my variable inductance primary coil and variable
secondary toploads - but to this point I have had no luck.  Now I am
going to try either A) Running calculations on all my values, B)
Attempt troubleshooting it with a scope at low power or C) Using a
different circuit.

	On to the schematic - on D.T.'s drawing watch out for the large .85uF
bypass cap - it seems that value is way too high.  I used a .01uF mini
MMC and that seems to work better.
	Also when you wind your primary coil, I'd recommend that you put your
taps at the bottom of the coil if you put your feedback coil above the
primary.  Or on the flipside, put your feedback coil below your
primary coil if you want to tap the final 10-30 turns.  This is so
that when you change your tap-point you don't also change the coupling
to the feedback coil!  When I built my vttc, I didn't do this and I
think that is causing some problems.
	Also, I included the LR plate protection combo, even though it was
not shown on his circuit.  I did like most and wound a few high-gauge
turns of wire around a ~50 Ohm resistor.
	For your grid-leak resistor, I would recommend using the lower
resistance (5k) - on my coil I used a variable high-wattage pot and I
have found that the lower resistances work better.
	And another tip - if your coil doesn't work the first time around,
try interchanging the leads of your feedback coil - it could be out of
phase!
	Keep in mind that adding more tubes will add more capacitance (from
the tube itself) so that will require some tweaking, but probably
nothing more than regular tuning.

Well, that's all I can think of for now... Good luck with your VTTC,
let us know how it goes!

-Andy C.
--------------------
Andy Cleary - KC2GVE
RPI Electronics Club President
AJAX Electronics
cleara-at-rpi.edu
Geek# 1010
www.rpi.edu/~cleara/
-------------------

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, September 28, 2002 3:54 PM
To: tesla-at-pupman-dot-com
Subject: VTTC/ would this work?


Original poster: "Steven Ward by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <srward16-at-hotmail-dot-com>

I found that Alan Jones has a very simple 811A circuit.  Here it is,
but
look at the values i intend to use rather than what he has:

http://personalpages.bellsouth-dot-net/a/j/ajones18/811Aschematic.jpg

T1- 2000v MOT
T2- 6.3v 3A filament transformer( i know i need 4A, Fair radio sent me
the
wrong transformer!! is this a problem, it worked before)
C1- 940pf 20kv doorknob
C2- 900pf 8kv Poly caps.  (would 6kv be acceptable? i could get more
pf
then)  I also have a .01uf 10kv cap, but this seems way too big.
L1- 30 turns of #14 solid 6.25" diameter.  Tapped on turns 10-30.
L2- 25 turns of #24 magnet wire 6.25" diameter.  No taps (is tuning
needed
on this coil?)
L3- 2 3/8" diamter.  12" wraped with 28awg magnet wire.  Unknown
topload
L4- 10 turns of wire on R2
R1- either 10kohm 10 watt or 5kohm 20 watt, whats better?
R2- Is the L4 R2 combo even needed?  If so i guess i'll shoot for
about
50ohms

David Trimmel uses a very similar circuit with 2 803s.  He does not
use the
L4 R2 combo. Does the primary sit below the grid coil(opposite the
diagram)
Also, if i were to add a second 811A, will the coil be in tune still?
or
will i have to change any of the components values(besides re-tuning
the
primary)?  Thanks guys, i know that ive been posting alot and changing
my
mind on just about everything, but this looks promising.

Steve Ward.

_