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Re: dorm freindly project (fwd)
---------- Forwarded message ----------
Date: Thu, 02 Aug 2007 11:21:55 -0400
From: Shad Henderson <shenderson@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: dorm freindly project (fwd)
Hi Scott,
What you want is a bipolar vacuum tube tesla coil.
The bipolar design eliminates most of the RF, and eliminates the need
for a dedicated RF ground. Not needing an RF ground is a great feature
of bipolar coils.
For a tube, I'd recommend a sweep tube. Plate voltages are 300-600V
usually, and plate dissipation runs from 15-30 watts. Figure it'll
process 100 watts without any trouble, and sweep tubes will generally
take one hell of a beating. Most are 6.3v filament. Don't fret that
they're beam power pentodes. A resistor between the plate and screen is
all that's needed. Just calculate the voltage drop and current, and
size the resistor accordingly to dissipate the heat. Sweep tubes are
generally much cheaper than transmitting triodes, also. (the 811A
requires a socket, higher plate voltage, and if the plate gets red, the
tube usually outgasses, becoming very weak)
Most sweep tubes use an octal socket. That simplifies things a lot
also. I personally use octal relay sockets. They mount to panels or
DIN rails, and can handle 600V. Much more than that, and I recommend
investing in a ceramic socket. For top cap clips, you can buy the
proper item, or use a cheap fuse clip. Make sure to insulate the top so
you can't accidentally touch it.
For a plate supply, use a 120:240/480v control transformer, rated 75VA
or better. I got mine from a wholesaler for about $35. They're fairly
cheap, and generally robust.
For tank caps, use an MMC just like a spark gap coil, just use much
smaller values of capacitance. A few nF is all you need. Same with the
grid leak cap. For the grid leak resistor, hit www.allelectronics.com
and buy power resistors. You'll want about 10-20% of your total input
power for dissipation (my rule of thumb, your mileage may vary.) Stay
away from the aluminum encased power resistors. They are *highly*
inductive, and tend to explode when abused badly. Trust me.
For a secondary, I generally use 2" PVC wound with 32-26ga wire, about
15-18" long. I buy craft foam discs and shape them with a rasp to
toroid shaped, cover them with aluminum tape, and use them as corona
suppressors, and 18ga solid copper wire for the breakouts.
For the primary, I use any convenient sized PVC pipe wound with 18ga
THHN. For the supports, I use plexiglass or lexan, and silicon to glue
it all up. I use two pieces of lexan, with either a hole for the
secondary cut in them, or a "U" shaped cradle cut in them. I glue the
primary coilform between them, then glue the whole mess down to the
base.
Line filters are cheap for 120v 10A filters, so include one of those,
and of course, fuse the input. Wiring between components is usually
18ga THHN, crimped and soldered. Be sure to crimp *and* solder the
plate connection. It can sometimes get hot enough to melt solder. Been
there, done that. Exciting, scary, and dangerous.
Use 2 switches for power. One for the filament, and the other for the
plate supply. Slave the plate supply switch off of the filament supply
switch, so that if you have them both on and turn off the filament, it
also kills the plate power. Helps to protect the tube.
The bipolar VTTC puts out little RF, produces longer streamers (between
the breakouts) than a traditional vertical coil, and can still light
florescent bulbs. They run quietly (unless the tank cap explodes), and
don't need a dedicated RF ground. Best of all, by using sweep tubes,
the whole setup remains compact for storage or transportation.
Besides, tubes are *much* tougher than solid state, and an IGBT just
can't match the coolness factor of a tube with it's filament blazing
yellow and it's plates glowing red as sparks snap and hum from the
coil.
But beware! Touching the output is silly, and dangerous. You'll get RF
burns from it without feeling a thing. It can and *will* set fire to
anything that the arcs hit, and can muck up electronics if they're too
close.
Hope it helps!
Shad H
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On Wed, 2007-08-01 at 15:11 -0600, Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Wed, 01 Aug 2007 16:34:06 -0400
> From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: dorm freindly project
>
> Hey guys.
> As I will soon be going back to school, and living in an apartment with
> 2 people and have neighbors for the first time in my life, I am in need of
> some sort of project to keep me busy (yes, I do have homework, but man can
> not live by homework alone!). Naturally, I want to build another TC, a
> small one, but it needs to make minimal RF interference, less noise (so a
> conventional spark gap coil is probably out) and be simple enough for me to
> understand (I have never tried solid state before), and cheap enough for me
> to afford (all college students are poor, unless their mommies pay for
> everything. Mine doesn't). So, all ye out there with experience, what
> would you recommend as a dorm friendly project, or am I stuck with flyback
> plasma globes (which are still fun, but lack the awe inspired by untethered
> high voltage). Thanks.
> Scott Bogard.
> P.S. My neighbors may not all be students, so I cannot use "you have your
> loud music, I have my TC" as an excuse for too much noise, but a little
> should be acceptable during the daytime. Thanks again.
>
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