Voice Modulation

To: tesla-at-pupman-dot-com
Subject: Voice Modulation
From: "Mike Nolley" <nolleym-at-willamette.edu> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Mon, 15 May 2000 07:58:14 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

    I have a question for all of you who are familiar with voice modulation of
VTTC's.  My current project is to build a poulsen-arc driven CW coil which will
also (eventually) be voice modulated:  the problem is that there is no grid
current to vary--and supply circuit modulation is out of the question (the
amplifier would have to be huge).  The solutions I am aware of are the ones
that were available to Poulsen and the early CW radio pioneers.  In the
Cyclopedia of Applied Electricity (circa 1911) they describe several types of
resistive modulation via carbon microphones, either introduced directly into
the circuit, or inductively coupled to it.  The problem is that the carbon
microphone can only handle so much current, consequently the variations in the
signal could only be as strong as the maximum current that could flow through
the carbon.  If I were to simply use resistance modulation, I'm pretty sure
that I would get little if any "audible" modulation in the spark.
    In order to get a more powerful signal, it would be necessary to modulate
the supply output with a modern amplifier inductively coupled to it.  The
filtration issues are no small problem--and the technical aspects I'm really
not familiar with either.  My thought was to introduce an iron core into both
of the DC charging reactors, and vary the inductance through "control winding"
that would be powered by the output from any old stereo amplifier, suitably
filtered of course.  But that's just my seat of the pants reaction--I'm a hack
when it comes to basic circuit theory.  Comes from being a philosophy major I
guess. . . ; )  Can you guys help me out?

                --Mike