"Ross Tucker, NS7F" wrote in message
ups.com...
A little over a year ago, I posted a request for help (1) in designing
a circuit to get 300VDC out of a power supply that was pumping out
~520VDC. I got many helpful replies, but unfortunately, I was unable
to complete the circuit. I now have three transmitters (2,3,4) that
would like
a nice source of high voltage and I must now admit that I really do
need your help in completing this project.

I own a really nice, heavy transformer that I'd like to use-
unfortunately, the voltage is a bit too high- it puts out ~520VDC
(after a 3-pole filter 10uF/10H/10uF with 40kOhm bleeder
resistor). I am looking for some ways to bring this down to the
voltage I need.

Although I consider myself a competent builder, I am unfortunately not
much of a designer - this is what has prevented my progress for the
past year! I own the '05 ARRL handbook and Art of Electronics, but I'm
just not comfortable doing this myself. Specifically, telling me the
type of transistor/tube and not specifying the part number or an
article describing a similar HV regulator would leave me somewhat
stranded. I know I'm asking a lot here -- please understand that I
am immensely greatful for any of your help!

Here is my specification / wish-list, in decreasing order of
importance:
* produce ~370Vdc at 120 mA
* cost less than $50
* not require modification of the transformer
* also be able to produce ~240Vdc at 40 mA
* also be able to produce ~300Vdc at 70 mA
* be hollow-state
* be elegant

References
(1) One link to this thread is at
http://sci.tech-archive.net/Archive/.../msg01268.html
(2) The One-Tube Three-Band Novice Transmitter: see
http://www.bignick.net/Morgan_Radio/Radio_11.htm and download the
article on the mid-bottom right side of the page.
(3) The Novice Special transmitter: ARRL members only, download at
http://www.arrl.org/members-only/tis...df/71hb181.pdf
(4) The Simple Transmitter: ARRL members only, download at
http://www.arrl.org/members-only/tis...f/55ra019t.pdf


Do you need to have all three voltages simultaneously?
How good a regulation do you need?
How much do the current requirements vary on each voltage?
Will your supply support 570 volts at 230 ma?

If the currents do not vary much, then why not use a different resistor in
series for each desired
voltage? e.g., 1666 ohms at (at least) 24 watts, 10750 ohms at (at least)
17.2 watts, and 3900 at (at least) 18.9 watts. For confidence you might
wish to use a 50 watt resistor for the first and 25 watt resistors for the
second and third. You could have different voltage terminals for each
desired voltage. If the voltage decreases under load, then change the
resistance calculations.
Ed, N5EI