Re: Series-Pass tubes - Class C Audio Modulation

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

Original poster: "S.J. Cook by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-g8cyerichmond.freeserve.co.uk>

Many years ago I used an npn transistor as a series modulator in the cathode
of a 10W  VHF transmitter. The device was only a BFY51 but it worked! Can't
remember the details, but it used to be a fairly common approach, avoiding
expensive modulation transformers etc. I even used a carbon microphone
connected directly in the cathode circuit, I wonder if anyone has thought of
that as a method of modulating a small vttc, mind you I'd want a fairly long
lead on the microphone!!!
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, April 03, 2003 1:19 AM
Subject: Series-Pass tubes - Class C Audio Modulation


 > Original poster: "Mccauley, Daniel H by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >
 >  >>> Could you recommend some tubes which would be available to use as
 > Series-Pass tubes???
 >
 > Thanks
 >
 > The Captain
 >
 >
 > A slightly better technique is series modulation where you leave the
 > oscillator in class-C but bring the supply voltage in through a
series-pass
 > tube. By modulating the grid of that tube you make the B+ go up and down
in
 > time with the audio. For maximum undistorted output, you make the
quiescent
 > supply voltage half of what your power supply gives: 25% power again. If
 > you were regulating the power supply anyway, you could modulate the
 > regulator tube.
 >
 > Steve C.
 >
 >
 >