dynamic power changing on TC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Any ideas on how to implement a rapid response (10s of milliseconds) 
"volume control" for a spark gap type tesla coil (at constant break rate)? 
(It's fairly straightforward for a VTTC...essentially a high power AM 
modulator)

Some ideas:

Adjust the voltage being fed to the primary which would change the "bang 
energy". Assuming you're using a triggered spark gap, what sort of voltage 
range can work... Easily 2:1, but can you get more?  Those of you running 
triggered gaps, what interaction have you noticed when running the variac 
up and down?  With resonant charging, this is tantamount to a power 
amplifier with multi kilovolt output, but at least it's in steps.

Adjust the tuning of the coil, for which I can think of at least two ways 
to do it:

Multiple primary taps with separate triggered gaps connecting them to the 
primary capacitor.  You would fire the "optimum" gap to get the most 
energy, and one of the "non-optimum" gaps to reduce the output voltage 
(because the fres of the Pri and Secondary would be farther apart, and 
you'd reduce output power), even though the primary cap energy remains the same

Some sort of "off axis" inductor or capacitor switching scheme with some 
suitable switch device (which doesn't have to respond at RF, just pass RF...)