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

"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

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.


As a first, simple, experiment disconnect the 10uF nearest the rectifier and
reconnect it in parallel with the other 10uF. Then see what DC voltages you
get when drawing currents between 120 and 230mA. If it is near enough to the
370v you require, then add suitable resistors to deliver the other supply
voltages and currents you've specified and you've got what you need.

John A wrote:
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.


As a first, simple, experiment disconnect the 10uF nearest the rectifier and
reconnect it in parallel with the other 10uF. Then see what DC voltages you
get when drawing currents between 120 and 230mA. If it is near enough to the
370v you require, then add suitable resistors to deliver the other supply
voltages and currents you've specified and you've got what you need.
=====================================
Suggest you have a look in the ARRL magazine QEX ,July/August 1999 ,
pages 51 through 55.
"A regulated 2400V Power Supply" , by VE6AXW

In this supply unit the output voltage is controlled by silicon
controlled rectifiers (SRCs) in the primary (120 or 230 V) winding

The principle of this scheme can be readily used for your 370V-DC power
supply .
The output voltage can be set to any voltage lower than the one provided
by the rectifier(bridge) in the secondary winding at the full supply
voltage to the primary winding.

For the other 2 lower voltages you need you can use a zener diode
/resistor arrangement with or without a high voltage ( use low cost 1500
V type)transistor if you really need a constant voltage at varying load.
Otherwise the lower voltages can be obtained from resistors, as per a
previous message in this thread.

The transformer must of course be able to supply the total current you need.
If you don't know the max current which can be drawn from the
transformer , you first measure the no-load output voltage and
subsequently load the secondary winding with suitable resistors until
the voltage has dropped by 5% The relevant current can then be taken as
the maximum for the transformer (practical approach)
The max current check can of course also be done with the
rectifier(bridge) connected (DC measurement)

Frank GM0CSZ / KN6WH

"John A" wrote in message
...
As a first, simple, experiment disconnect the 10uF nearest the
rectifier and
reconnect it in parallel with the other 10uF. Then see what DC voltages
you
get when drawing currents between 120 and 230mA. If it is near enough to
the
370v you require, then add suitable resistors to deliver the other supply
voltages and currents you've specified and you've got what you need.



I second dropping the first filter capacitor. It will lower
the voltage and reduce the strain on the power transformer
as well.

Pete

On Apr 20, 12:18?am, "Ross Tucker, NS7F" wrote:


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.


Let's start at the beginning.

You have a power transformer and a rectifier, followed by a C-L-C
filter (aka capacitor input). And you're getting a bit over 500 VDC
from it.


1) What rectifier circuit are you using?


a) full-wave center-tap
b) full-wave bridge
c) voltage doubler
d) some other type (specify)


2) What sort of rectifier(s) are you using?


a) High vacuum diodes (5U4G, 5Y3GT, 5R4GY, etc.)
b) Solidstate silicon diodes (1N4007, etc.)
c) some other type (specify)


3) What are the transformer ratings, part number, etc.?


4) Which of the listed transmitters have you built?


73 de Jim, N2EY