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oups.com...
Hi all,

You may recall me mentioning I was thinking about adapting a 24V PSU
for use at 13.8V for powering up mobile HF rigs and stuff. I had some
spare time yesterday and took this thing to bits for a better look
inside. It turns out the mains transformer has several secondary
tapping points. I discontected the DC-stab/reg side of the supply
circuitry and reconnected the secondary tapping points to lower voltage
tappings.
Now I measure 16.8V after the transformer's output has been rectified
and applied across the *big* electrolytic. This is under no-load
conditions. Now, is that 3V enough 'headroom' to use up in regulation
and stabilisation for 13.8V final output if I throw the old 28V
reg/stab away and build something from scratch? There are 6 pass
transistors plus a driver (2n3055) already mounted which I plan to use
in the adapted version, so basically I'll just junk the existing
control board and re-use everything else. Any observations/tips?
Thanks,
P.

I would cobble together a simple, say lm317 regulator to drive your series
pass driver and see what you come up with under some small loads. You may
be ok with that big transformer. The power supply I built uses 4 2n3055 in
parralel like what you have. Have fun.. JTT

James Thompson wrote:
I would cobble together a simple, say lm317 regulator to drive your series
pass driver and see what you come up with under some small loads. You may
be ok with that big transformer. The power supply I built uses 4 2n3055 in
parralel like what you have. Have fun.. JTT
===========================
There as an exellent design in RadCom Oct 2001 ,pages 34-35 by OZ1XB ,
with a LM317 , TIP32 (PNP) and 2xBUV20 (NPN) ,with the latter
replacable by 4x2N3055 or whatever you have .
Simple,rugged ,reliable design.
It incorporates sensing lines ,ensuring the full set voltage under all
load conditions at the consuming apparatus.

Frank GM0CSZ / KN6WH