Hi,
Assuming that the P.S. is operating normally; I would use a string of
silicon power rectifiers in series to reduce the output. A silicon
rectifier (any kind) will have a .7 volt drop across it. Three in series
will give a drop of 2.1 volts. 16volts minus 2.1 equals 13.9 volts. Close
enough to the classic 13.8 vdc. Or if want add another in series then you
would be down to 13.2 volts. I would go with the 13.9 vdc.
You did not mention what TT equipment, I assume a 100 watt transceiver. I
would use 25 amp diodes at least and mount them on a heat sink. These
diodes are very cheap, and check their temperature by hand.
Check with JOHNSON or a Johnson two way radio shop for a schematic. Locate
the voltage regulator and with a change in ONE resistor you could drop the
voltage. If you can read the letters/numbers on the IC's. (LM-340, and 723
are common ones) I might be able to tell you what resistor to change.
Check to see if you find any pots. If you see two, one would adjust the
voltage and the other the crow-bar point, (voltage above the normal at which
the PS shuts off)
GL and 73 Ken WA4RPH
PS. If you dont know the source of the PS it could be defective and
discarded by some tech. Safest is to assume it is bad unless proven it is
not. Caveat emptor.
-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com]On Behalf Of Rich Gaarden
Sent: Sunday, February 23, 2003 3:24 PM
To: tentec@contesting.com
Subject: [TenTec] Johnson PS ??
Hi Folks,
This is off topic I suppose but the PS will be used on Ten-Tec equipment!
I acquired a very heavy 40# perhaps PS which is not properly regulated (16
V). I was told it was from a repeater and that it was a Johnson 30 amp
continuous. I thought this would be an easy fix.
There are heavily heatsinked diodes. There is a substantial choke and
appropriate filter caps. There is a large two section transformer. There is
a small section which vaguely resembles a VR but there are no pass
transistors. Anyone know how this thing might work? Could it be a
saturable reactor? Any one know how to regulate the output?
I realize that I'm not giving a lot of information but perhaps enough for
someone to point me towards help. I have worked on a few supplies but never
one like this!
Thanks,
Rich KF3DQ
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