RE: [TCML] Tube choice for a VTTC

["James" <mustang3@xxxxxxx>]

There are old tube manuals "out there". I have some on paper (arrl
handbook), some on cd's, and found some on the internet. The reason we
want a low mu tube is what you stated. The high mu tubes are mostly for
grounded-grid linears. The high mu is more sensitive to the bad stuff
showing up on the grid. The streamer induces nastyness back into the
tickler coil. By hard biasing the tube off, we hope to either suppress
or bury the + going nasty stuff. I suppose that you can tune your VTTC
to work successfully with about any tube. Just falls into the more time
category. Due to frequency splitting, neither the primary or tickler
coil are exactly tuned to the secondary's frequency. Both of my VTTC's
have the primary frequency set a little below the secondary frequency. I
always tune the tickler starting with 30 turns or so. Then I use a
variac on the plate supply, bring the voltage up slowly, and observe the
grid waveform on my o'scope. This way you can prevent any undue
aw-s***'s. Are you going to self rectify the plate supply or use a
bridge? 120Hz sounds cool. My 1st coil used an 811. Man do those things
burn up fast! My absolute fav for all time is a 304TL. They are a work
of art in glass. Four of them in parallel is good for 1200 watts plate
dissipation. Enough heat to warm your house. lol I broke a few, don't
think I killed any tesla coiling. Check out the waveforms on my vttc
video: http://www.youtube.com/watch?v=7Ky4a9KPlVY
I'm going to post a video of my horizontal VTTC soon. All of it's coils,
tickler, primary, and secondary are very closely coupled. When it's
sparking, high amplitude spikes show up in the grid waveform. These
spikes are + and - in amplitude. So the grid has both out of phase and +
spikes. Yikes! Good luck. James 
 

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of David Speck
Sent: Sunday, June 14, 2009 7:53 AM
To: Tesla Coil Mailing List
Subject: [TCML] Tube choice for a VTTC

List,

I've read previously that the best tubes 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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