Re: CW coil top terminals?

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

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



Tesla list wrote:
> 
> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
> 
> Hi Jim,
> 
>         I looked up the control input bandwidth and it is 1.6Hz :-p
However it
> has very fast internal control loops so maybe it can be whipped up some at
> least for staccatto work.  I'll pull the schematics and grill the designer
> about getting it the run faster.  It is a PDX plasma supply so it has very
> good control and bullet proof protection.  A real linear amp would be a
> dream machine with an ARB if it would not blow up.  I know Hams and radio
> guys use wide band amps but I am not sure one of those would work...  If
> there are any good choices for a cheap wideband amp, I would be interested
> in checking into it.  My TC budget will be a little streached after getting
> the ARB and a few other toys I really need :-))
> 
> 

Even a fast modulator might be a nice way to go, driven by a high power CW
source.  You could use a PC sound card as the ARB.  There are PIN diodes
that can take kilowatts (of course, you'll need a pretty hefty PIN diode
driver to make it work..)

Most Ham amplifiers are quite narrow band, partly for efficiency, and
partly for harmonic suppression (they run Class B or Class AB).  


However, there are some broadband solid state amplifier designs around
(Motorola Engineering Bulletins), and at lowish frequencies (<3 MHz), the
devices shouldn't be all that expensive (so you don't have go out and buy
those MRF454s at $100/pop). 

If you don't mind horrible efficiency, then a fairly simple Class A
amplfier with a BIG power supply might do the trick quite nicely.  

I wonder what sort of output impedance you'd want to design for?
Typically, you drive the primary with a few hundred watts at 10-20 kV,
implying a load impedance of several hundred K ohms.  Seems like a suitable
Class A (or maybe a Class B push pull) tube amp might be the way to go.  I
gave away a set of 4 4CX600 power tetrodes that I scrounged... I knew I
could do something with them....

Or, try and design a broadband transformer to bump the fairly low output
impedance of a transistor amp up to the right levels, but that might be a
bigger challenge than the tesla coil itself. If you go the easy way and use
tuned circuits for the impedance transformation, you might find yourself
learning more about the behavior of your coupler than of your tesla coil...
 On the other hand, a LC tuner/impedance transformer, and some good
instrumentation on the actual TC primary, along with the ARB might not be a
bad scheme.  You can always adjust the waveform going into the amp until
what comes out of the ARB/amp/transformer looks "right"...