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Fred McKenzie · July 15th 08, 07:24 PM posted to rec.radio.amateur.homebrew

In article
,
wrote:

The voltage gain of the
darlington transistors is less than unity in this case since they are
being used as emitter followers.

Jimmie-

I agree. Being the devil's advocate, a circuit can have parasitic
elements you don't think about, and can oscillate in a different mode
than it normally operates in. If you were using it to power a
transmitter with a poor antenna, there might be some RF energy entering
the base-emitter junction. The energy is rectified and shifts the bias
conditions. DC output voltage is changed, resulting in a change in the
level of the rectified RF, resulting in a change in the DC output
voltage, et cetera. Normally you would disregard this until/unless you
actually observe a problem.

I agree with Paul, that you want the capacitor voltage to be relatively
close to the output voltage. But there is a limit where hum starts to
appear in the output, and regulation is reduced. In the case of the
Astron RS-20 circuit diagram, the main capacitor voltage is listed as
23.0 for no load and 18.0 under load, for 13.8 VDC no load output and
13.7 VDC under load.

I worked on a friend's RS-20. After repair, I ran it for several hours
at 8 Amps load. This is within the continuous power rating, but the
heat sink really got hot!

Fred
K4DII