Re: CW coil top terminals?

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Duncan,

I would think that a TC speaker/tweeter would also suffer from the
background noise of the plasma.  I have run the output of a radio into the
level control of power supplies under arc to play music with the arc.
However, the sizzling of the arc almost drowns out the modulated music
signal.  You can hear the music and recognize the words and song but I
don't think it is ready for the audiophile world :-))

However, as a stage stunt, it may be really neat for a haunted house
attraction to be able to say words with the arc.  Having the arc sound like
a blood curdling scream would probably add to a few more patrons being
carried out :-))  Perhaps, if the lobster in Fox news story could have
talked too... :-))  There would be a number of purely fun uses for a real
talking Tesla coil.  Your bandwidth concern is very valid but either a low
bandwidth voice signal could be used or reduced modulation.  Fortunately,
well controlled CW coils can be run fairly quiet so a voice signal by be
quite clear if not of musical quality.

I am looking into running a coil now from an ARB and high power wide band
amplifier for total input signal control.  Such a talking coil stunt would
be trivial once such a system could be made.  It could mix the Fo carrier
with any audio signal.  I think if you also cut frequencies below say
100Hz, the output would be very stable.  More to work on there...

Cheers,

	Terry


At 06:26 PM 1/31/2001 +0000, you wrote:
>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
>