Re: CW coil top terminals?

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

Original poster: "David Trimmell by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davidt-at-pond-dot-net>

Terry, Duncan,

Audio output volume was never a problem, the fizzling of the spark was 
drowned out by the Audio. The problems I had with distortion were more with 
the base frequencies. I used a old solid state Tuner/Amp that had Treble 
and Base controls, I was forced to run with the Base all the way down, 
otherwise the tube would run to cutoff (modulation side bands) and Audio 
would be clipped.  This seemed to be more from the low frequencies than the 
amplitude...
High Base signal would make the spark more like a pulsed VTTC than a CW one.

Should be a piece of cake for you Terry ;-)

Duncan I think your thoughts of the "modulation asymmetry" is probably 
right on target. I need too do more research on this... I wish I had some 
of the neat toys that Terry's got :-). I think the frequency response of 
the spark may not be ideal for low F Audio, probably why there are plasma 
"tweeters", not plasma sub woofers!  I appreciate your input.

This has been worthy, but frustrating project. I finally burnt out the 
Solid State amp, but I have a old Heathkit AA-181 that I modified to run 
off of 6L6's, as the original 7591A's were bad and to expensive to replace. 
It's only rated at 25 watts, but I have confidence that it'll work.

Regards,

David Trimmell
www.ChaoticUniverse-dot-com




At 11:31 AM 1/31/01, you wrote:
>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
> >