[ARC5] SS Cathode modulator.

[Fuqua, Bill L]

  It will work but with a ceramic or crystal microphone and since it uses a 3 transistor darlington driving the base of the power transistor directly the cathode current will
be very unstable and it will be very distorted as well with splatter. And that is with a modern transistors. Perhaps by connecting the bias resistor to the collector/cathode terminal and
a resistor to ground from the input base to ground it will become more stable, and more linear.

  73
Bill wa4lav
________________________________________
From: ARC5 [arc5-bounces at mailman.qth.net] on behalf of Kenneth G. Gordon [kgordon2006 at frontier.com]
Sent: Monday, October 12, 2015 8:56 PM
To: Arc5 at mailman.qth.net
Subject: [ARC5] SS Cathode modulator.

Actually, from reading the blurb which accompanies the circuit, it would
appear that all it does is control the cathode current of the tube(s) being
modulated.

In other words, Q-4 is an audio-controlled variable resistor in the
cathode-to-ground circuit.

The 6 volts has nothing to do with it there. That simply provides operating
voltage for the other 3 transistors. Current drain from the 6 V source is
minimal.

The other 3 transistors simply drive the base of Q-4 and are connected the
way they are so that they present a high-impedance at the INPUT.

R-1 sets the quiescent current through Q-4 at no modulation.

Although I am still not sure about it, I'll bet it does work.

As I said, I'll bread-board one of these up and try it out as soon as I can.

If anyone else feels like trying it, go ahead.

Ken W7EKB
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