Phil Clements wrote:
>
> -----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 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
>
Lets talk about overkill a bit.
FWIW, back in my youth, (1969) as a new advanced I wanted a bit more
"umphf" on the low end of 20, so I went scrounging.
First hot item was a 7200VAC/ct transformer with taps at 5500, and
3500, at 3.5 AMPS!! with a multi-primary. My kind of transformer, but
at something like 150lb, it wasn't easy. (A young mans braun is usually
more than his brain can handle.) $25 and it went home with me. Next
item was a filter cap. 100MFD @ 3kv, oil filled about the size of a one
gallon paint thinner can. $5 each at the local surplus store. Took 4
of them home. Filter choke? Yep, 8HY at 2A, very large, VERY heavy,
rated at a max of 5kv. A GIFT!! Now on to the rectifiers. Lots and
lots of diodes with equilization resistors and caps across them. That
board was almost 14" long and 6" wide for each side of the full wave
rectifier. End Result, 200MFD @ 6KV filtering, and used 117VAC across
the 234VAC inputs and it came out at about 2500Volts DC and didn't drop
more than about 50V from no load to full load on the old pair of 813's.
Most of that was probably in the primary wiring of the apartment we
lived in. Granted not much current draw there, (DC) but for my money,
more stored energy is better. BOY DO I WISH I STILL HAD IT NOW!!! Sold
the hole amp to a friend when I moved away from home for $50!! Duhhhh!
Recently aquired a NEW, still in the box, TenTec Titan power
transformer and a large bank of 1 pound coffee can size electrolytics
mounted on a piece of lexan with all the terminals shorted by 5 watt
50Kohm resistors. 12 Each cap, 4700MFD @ 500VDC. I think I'll have
enough caps to keep most anything I build well filtered. ;+} Just going
to need a step start system on the AC line to keep from killing the
transformer with the start up current. Thinking seriously about using
either 4CX800 or maybe a 8877 Med-Pull. I like the idea of using less
than full, (100 Watt) drive to acheive 1500 output. Makes RTTY and SSTV
more apealing when you know you aren't overtaxing your exciter at
half-output or less.
Anyway, my opinion is that when it comes to keeping the voltage well
regulated and lots of reserve power for voice peaks, use bigger caps.
Worked for me.
Flame suit on, let her rip boys!!
Mike Baker K0QZ/7
Phoenix, AZ.
(Its so hot here in the Summer, Hell looks like a tropical vacation!)
(Where Air Conditioning isn't a way of life, it IS life!)
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