Re: CW coil top terminals?

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

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Marc, Jim, David, Finn et al!


Date: 30 January 2001 02:43
Subject: Re: CW coil top terminals?


Thanks for all the interesting info and links posted on this
expanding topic!  I'm delighted to know that the plasma
loudspeaker/singing Tesla coil is still very much alive and
well.

Jim/David, I'm wondering if some of the distortion in the
singing Tesla coils (STCs - now we have another
abbreviation;-) might be due to bandwidth limiting.  If the
sidebands go off to plus/minus 10kc/s say, and the nominal
operating frequency of the Tesla secondary is 100kc/s then
the Q can only be 100/20 = 5 at most to give clean sound (OK
it's a crude calculation, but it ought to be "ball park")
and I suspect that a cw coil is a bit more than this.  The
plasma tweeters use a much higher radio frequency, tens of
Mc/s in the examples shown in the links posted to this list.
They also use screen grid modulation which is inherently
limited in modulation depth - I suspect that a STC can't
approach 100% modulation because the plasma/sparks will tend
to extinguish at a higher voltage level than the troughs of
100% modulation and if your coil happens to use a high
modulation percentage, that also might be giving distortion
trouble via modulation asymmetry.  Unfortunately, low
modulation percentage equals low sideband power equals low
volume . . .

I recall seeing some simple ideas for monitoring modulation
depth in an old edition of "Hints & Kinks for the Radio
Amateur" published by the ARRL back in the 50s when AM was
king, using a magic eye tube as indicator.  If there's a
call for it, I'll see if I can find the circuit diagram.

Dunckx