[GreenKeys] OT: Tesla and Vacuum tubes

[John Lawson]

  A 'real' Tesla coil is a high-Q resonant transformer circuit that is 
impulse-excited.

   The electrical breakdown of an air-gap has one of the highest rise-times 
known... from a very high impedance to a few ohms in nanoseconds... much 
much faster than can be obtained with thermionic (vacuum tube) or 
solid-state technologies. Plus an air-gap can be easily made to handle 
hundreds of kilovolts at thousands of amperes - a good trick for any SS 
device!

   So the purpose of the air-gap in a Tesla system is to allow the energy 
storage devices (usually capacitors) to charge, then 'dump' that 
accumulated charge as quickly as possible into the resonant system.

   It's as if we have constructed a 'bell' - and the harder and sharper we 
'ring' that bell, the louder and longer it sounds...   so using an air-gap 
in a standard Tesla coil provides the sharpest, highest rise-time impulse 
excitation of the highly resonant transformer(s) that make it up.

    Rotary gaps can be used to "tune" the impulse-train so that the system 
Q and resonant frequency, AND the subsequent harmonic structure, can all 
be brought "in phase"  - which produces the maximum effect - throughput if 
you will.

   Most of Tesla's systems, Colorado Springs and Wardenclyffe especially, 
used large synchronous-motor rotary gaps and big arrays of HV capacitors - 
in those days generally he used banks of jars or bottles with a brine 
solution for the 'electrodes' - he experimented with the best glass and 
types of jars, and had two or three jar manufacturers supply him with 
same.

   A modern Tesla builder is here : www.ttr.com  and I have owned more than 
one of Bill's coils - the latest is the "Model 2" , if anyone is 
interested.


   A pleasant, safe, and prosperous New Year to everyone!

Cheers

John Lawson KB6SCO
Carson City, NV


obGreenkeys: RYRYRYRYRYRYRYRYRYRYRYRY!