[Amps] 2500 uF at 450V DC for $10.00 each

[Phil Clements]

Power supplies for SSB service whose current requirements have large
peak-to-average ratios
usually make use of a capacitor filter system. This simple circuit
eliminates the resonant transcients
that are often found in LC filter systems, and, if the capacitance is
sufficienntly large, provides
adequate voltage regulation. There is a graph in Bill Orr's "bible" to aid
in computing the
proper value for the filter capacitor for best performance. First, calculate
the load resistance
(RL) by dividing the PS output voltage by the expected current flow to the
load. The following
are minimum capacitances needed for optimum regulation:

RL=700 ohms, filter C=200mfd
RL=1000 ohms, filter C=90mfd
RL=2000 ohms, filter C=80mfd
RL=3000 ohms, filter C=55mfd
RL=4000 ohms, filter C=40 mfd
RL=5000 ohms, filter C=30 mfd

For example, a power supply designed for a single 8877 amplifier, (4000
volts @ 1 amp)
would require a filter capacitor of  40 mfd for optimum regulation. A supply
for a single
4-1000A (6000 volts @ 750 ma) would require a 20mfd filter C. A supply of
2500 volts
@800 ma requires 55mfd. Adequare dynamic regulation for both SSB and CW is
obtained
with the above values. Little is gained by adding more capacitance, but much
is lost by having
less C.

The inrush is handled in any case by adjusting the delay in the step-start
circuit to allow for
the voltage to reach 2/3 of maximum before relay activation.

As has been stated many times, the proper selection of filter C, step-start
circuit, and glitch
resistor are very important in a successful and reliable end product. Every
project will have
its unique requirements. I won't get into glitch resistor selection, as the
Eimac paper is very
comprehensive on this subject.

(((73)))
Phil, K5PC