Re: THOUGHT ON Vacuum Tube Tesla Coil Design (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 11 Oct 2007 00:39:22 +0200
From: Martin Damev <mdamev@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: THOUGHT ON Vacuum Tube Tesla Coil Design (fwd)

Tesla list schrieb:
> ---------- Forwarded message ----------
> Date: Fri, 05 Oct 2007 11:41:05 -0700
> From: Ed Phillips <evp@xxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: THOUGHT ON Vacuum Tube Tesla Coil Design
>
>     The operation of a self-excited VTTC is affected by the interaction 
> between tuning, grid circuit coupling and drive, and streamer 
> formation.  A design using a master oscillator - power amplifier [MOPA] 
> should be much easier to adjust as one could set the grid drive level 
> and adjust the frequency and plate circuit tuning separately.  With such 
> a configuration it should be much easier to achieve optimum opewration.  
> If tetrodes are used for the power stage the grid drive required would 
> be quite moderate and the design becomes more practical than of a triode 
> output stage is used.
>
>     Just a thought - I'm no where near close to building such a coil.
>
> Ed
>
>
>
>
>   
Hi Ed,

In my opinion such a circuit would be difficult to realize.
The circuit should automatically adjust to the changing
resonant frequency of the loaded secondary. The streamer's
capacitance loads the secondary considerably. It would
be easy to sense the secondary base current and control the
master oscillator. I see difficulties rather in the power stage.
It should be some type of broadband amplifier. Mechanically
adjusting the output stage during spark formation would
obviously be to slow.

Years ago I planned a VTTC inspired by David H. Sloan's work
( "A Radiofrequency High-Voltage Generator", Vol. 47,  Phys. Rev. 1935)
The circuit would have an aperiodic primary and only the
tuned secondary as resonator . While such circuit would work
fine when unloaded or only lightly loaded, it is rather doubtful it
would work under real tesla coil conditions. After several experiments
and hundreds of calculations I gave up this design.

There were very few efficient broadband power amplifier designs with
transmitting tubes. They almost always used ferrite cores. "Chain
amplifiers" also known as "distributed amplifiers" using valves are
rather inefficient and unsuitable for tube coils.

Perhaps there are alternatives to the classical VTTCs with their
self-excited
oscillators. Let's see.

Regards,

Martin