-----Original Message-----
From: Doug Hall <kf4kl@ipass.net>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: Thursday, March 18, 1999 11:26 PM
Subject: [AMPS] Power Supply Progress & a question
>
>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
>
Going from 25 mfd to 30 mfd on my 3900 volt P.S. improved my
regulation by 200 volts when applying a 1.5 amp load. This can
give you a ball park idea of what a few more mfd might do for you.
Also, be sure to measure the voltage drop under load on the primary
side of the H.V. transformer. I have reduced mine to less than 1 volt
drop no load to full load by running larger wire from the breaker
panel to the amp. Most guru's say that 25 mfd is a minimum value
for a cap. input P.S. and 40 mfd is probably a little on the overkill
side. GL!
Phil
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