Re: Arc Transmitter

To: tesla-at-poodle.pupman-dot-com
Subject: Re: Arc Transmitter
From: Tesla List <tesla-at-stic-dot-net>
Date: Wed, 14 May 1997 00:58:42 -0500
Approved: tesla-at-stic-dot-net
Subject:  Re: Arc Transmitter
  Date:   Tue, 13 May 1997 23:06:28 -0500
  From:   "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>


> Date:          Tue, 13 May 1997 00:37:25 -0500
> To:            tesla-at-poodle.pupman-dot-com
> Subject:       Re: Arc Transmitter
> From:          Tesla List <tesla-at-pupman-dot-com>

> Subject:    Re: Arc Transmitter
>       Date: Mon, 12 May 1997 11:42:50 -0700
>       From: David Trimmell <dwt-at-efn-dot-org>
>         To: Tesla List <tesla-at-pupman-dot-com>
> References: 
>            1
> 
> 
> Hello,
> 
> "However, because the coil DOES radiate, running a high power
> modulated Tesla Coil could result in your equipment being confiscated
> and a nasty fine. This may be one experiment you'd want to skip. :^)
> 
> Safe coilin' to you!
> 
> -- Bert --"
> 
>  I am very interested in modulating a Tube coil and am unsure of how to
> go about it. I curently am running off of AC with the Tubes self
> rectifying for 60 PPS + to the plates, for voice modulation you would
> have to run it as CW, so with a fullwave rectifier and heavy filtration
> I should be able to get that, correct? This is running off of a
> Microwave oven Transformer (2400V-at-500mA). Now where would the Modulation
> circuit be? In the Grid leak circuit? You would need a audio amp? What
> power etc.? If anyone has done this or knows how I would, and others
> also I'm sure, would be greatfull for instructions.
>  Now as far as the FCC is concerned, as long as these devices are
> opperated with proper Faraday shielding, theres nothing they can do. I
> believe the most important thing is to not be a nuisance to your
> neighbers. Well, as little as possible!
> 
> David Trimmell
> 
 
David,

I have successfully modulated a vacuum tube TC employing a small (10 
watt) audio impedance step-up transformer (8 ohms to 70 volt line).  
I put a 60 watt audio power amp into the 8 ohm side and put the 70 
volt line winding in series with the existing grid-leak circuit.  I 
employed full wave rectification and filtering of the HV using about 
8 mfd.  I got negative modulation, meaning the loudest audio would 
drive the discharge to stop.  The weakest modulation produced the 
most brush discharge.  Nevertheless, for someone like me who was 
introduced to playing Beatles records backwards in the late 60's, 
this sounds O.K.

For maximum fidelity you would want to put a modulation transformer 
in series with the well filtered supply B+.  This takes a lot of 
audio power though.  You need a full 50% of the watts that you are 
running your oscillator input at.  Thus, for even a modest 1 kW TC 
you need a 500 watt audio amp.  That's a big amplifier!

One method which takes some R&D (dinking) is to employ tetrodes and 
modulate the screen grids.  This scheme will require the least audio 
drive power of all mentioned here.  Pick up an older (50's to 60's)
Amateur Radio 
Handbook and study the various modulation schemes employed in A.M. 
Telephony for ham transmitters.  The techniques are exactly 
transferrable to the vac tube TC application.

When you do get it operating, DO NOT MODULATE IT WITH RAP MUSIC
or  I will surely come and arrest you!

rwstephens