RE: [TCML] Tube choice for a VTTC 350khz?

["Jim Mora" <wavetuner@xxxxxxxxx>]

Hi John,

Was it Dr. Spark ?? or someone noted that if their coil was running @ 350khz
or above it had nice swords. Frequencies set below this were more brushy. I
suppose geometries and power must play into this too. I am designing my 4x
833c to run at ~350khz and still have 17-25 turns on the tank coil on a 10"
acrylic former. I hope that works. The coil will be 6"x24 wound with 21awg
to keep the turns down. Have you space wound this scenario? My top load may
end up being an edge rounded 7" .375 aluminum plate to keep the freq up. I
also have one of your 6" toroids to attempt to duplicate the freq difference
and arc shape changes. I have a very big tunable plate cap under oil which
should assist in attempting replication of this observation.

I would like to find a 4400 5kva pig or PT! There are some 15KVA pigs on
ebay. Too Big! My big, mutitap dry transformer is way too big too (over
200lbs). Anyone?

Jim Mora

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of futuret@xxxxxxx
Sent: Sunday, June 14, 2009 10:30 AM
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] Tube choice for a VTTC

Dave,

I think as a practical matter, just about any kind of power tube can 
work well
in a VTTC provided it's robust and can withstand the voltage, etc.  I've
used tubes such as; 833A, 833C, 803, 805, 810, 845, 304TL, 4-250A,
4-125A, HF300, HF200, etc.  All of them worked well.  Some coil designs
seem to require a lot more tweaking to make them perform well.  Some
designs tend to produce fuzzy sparks, whereas others produce spikey
sword-like sparks.  It's not completely known why this occurs.  There
is some evidence that a higher frequency helps to produce swordlike
sparks, but I know that other factors such as tube type, tuning, 
coupling,
and feedback all affect this also.

I think the addition of a small toroid to a VTTC may help to stabilize
the operation.  A toroid seems to help the spark output some also.

Perhaps at some point, someone will try to quantify all this, and maybe
make up some sort of computer design program to assist with VTTC
design.  Some of the known rules of thumb, formulas, and general
principles could be incorporated into the program.  I think there's 
still
a lot of unknowns about tube coil design and operation.

Cheers,
John


-----Original Message-----
From: David Speck <dave@xxxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sun, Jun 14, 2009 8:52 am
Subject: [TCML] Tube choice for a VTTC


List, 
 
I've read previously that the best=2
0tubes for VTTCs are ones with low 
Mu's or amplification factors.  
If one were to happen upon a high Mu tube at a good price, is there a 
way to adapt the VTTC grid or primary circuits to make it work well?  
Would using fewer turns in the grid coil or some sort of resistive 
voltage divider be sufficient to optimize performance? 
 
Does the high Mu make it harder for the system to remain stable when 
the coil is loaded by the streamers?  
Can anyone recommend a good reference book on the design of high power 
vacuum tube amplifier/oscillator circuits? Seems all I can find are 
books on guitar amplifier construction, a little small for my tastes.  
Thanks, 
 
Dave 
 
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