[AMPS] Power Supply Progress & a question

[Doug Hall]

Greetings all,
   Tonight I finally did some load testing on the power supply I'm
building for my homebrew amp project. (Pair of 3-500Zs.) The supply is
a full wave design with capacitor input (16uF 7500v oil filled), and
produces 3900v with no load. I can adjust this up or down some by
changing taps on the primary.
   I've got a resistive load (buncha big resistors) that I used for
testing, and by shorting out various resistors I can vary the load.
When I connect a 4K ohm load to the DC output the voltage drops from
around 3900v no-load to 3250v. At this point the current is a little
over 0.8A. If I decrease the load R to 3500 ohms, the voltage drops to
around 3200v for a current of just over 0.9A. The secondary voltage
drops about 350v from 5800v to 5450v AC, no load to full load. (Center
tapped secondary, rated 2800-0-2800)
   So here's my question: I have a drop of 350v AC on the secondary,
and a drop of around 650v DC at the output under full load. Does this
all sound OK, or does it sound like I need more filter C?
   I realize I don't need 900 mA for a pair of 3-500Zs, but this amp
is going to be used for RTTY contesting, among other things, so I want
a supply that's up to the task. During all my testing, nothing got hot
except the resistors.
Thanks & 73,
Doug, KF4KL


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