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Old 07-28-2012, 05:17 PM   #1
Jack Crow
Badcaps Veteran
 
Join Date: May 2008
City & State: Herndon Virginia USA
Posts: 609
Default Pyramid PS-36KX repair report

All,
Picked up a very used Pyramid PS-36KX today from a client.
A whole 30 bucks, cash and carry.

It's a big ham or CB 12 volt linear power source.
A variant of the classic LM723 regulator.

Took it home and started to play.
Clearly it spent time in a barn.
Full of organic crap and cob webs.

The client said it was dead.
I plugged it in and it worked with some problems.

First internal fan did not turn.

In it's past life, someone had worked the thing over.
They were un inspired and poorly informed.
The fan was wired into the 24 volt side of the regulator.
Too bad it was a 12 volt unit.

Removed the dud fan, and replaced it with something out of a modern PC power supply.
There is now a little control board and temp sensor in the thing.
So as the heat sink warms up, the fan speeds up.

The front panel voltage adjuster was snapped off.
Found a replacement at Radio Shack.
Now it can be drifted from 11.85 to 15.05 vdc,
Got a new knob so the thing looks spiffy.

Added lights to the meters, now they have a very soft red glow.

Noticed the amps meter was out of tolerance.
Adjusted it, now tracks properly. In fact better than the Astrons.

Voltage regulation is wonderful.
From 6 amps to 15 amps it drops 10mV.
No ripple can be detected worth speaking of.
The HP3456A shows me about 100 micro volts of AC under 15 amps load. More than good enough for radio use.

Even found a schematic on the web, will print it off and stuff it in the case.

It's not great, but it's better than some more modern junk I have had the duty to fix. This will make some client happy for the next five or six years.

So that's the news.
Jack Crow in Herndon VA
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