I was glad that I caught Jim's remark about blowing the 723 by being
connected to a battery with the PS off. And also Myron's answer.
Back in the tube TV days, I purchased a bare circuit board at Radio
Shack, (I think). The board was similar to an Astron circuit board, but
simpler. I rewound a heavy transformer from a color TV and made my
first 13.8 Volt power supply to use for a Heathkit HW-104. Years later,
the 723 went bad. It may have been due to the stated reason, I can't
remember now. I did some repair work on it and still have it.
Someone on the reflector provided the following link one time, which I
think is a good idea for an extra measure of over-voltage protection or
accidental reversal in polarity. I remember discussion about a reversal
that happened to someone on the reflector not long ago.
I hope the link still works on here. If it doesn't, it is on ad5x dot
com website. Look for a Vprotect pdf file.
http://ad5x.com/images/Articles/Vprotect.pdf
Dick, n0ce
On 7/21/2016 7:41 AM, Myron Schaffer wrote:
Jim and Clay,
It used to be that way....the RS linear models could not tolerate external
voltage present when unpowered, not anymore. Astron has incorporated
back-voltage protection through incorporation of some diodes installed in key
locations to prevent this.
You can verify if your supply has this modification by looking at the circuit
board and see a 1N4001 type diode soldered across 2-pins (can't remember which
ones off the top of my head) of the IC voltage regulator LM-723 chip and others
hung in various places to protect the pass transistor as well. Usually soldered
to the solder side of the circuit board so they are easy to spot. I can't
remember is there were some small capacitors added as well.
Any newer (like newer than 1990) linear Astron will have these installed.
Myron WVØH
Printed on Recycled Data
-
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
