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Model 250 Power Supply Unit

Hand-drawn schematic of Model 250 PSU

Reverse-engineered schematic of my 250 PSU.

Copy of schematic of Model 251 PSU

I can't remember but I assume this is a copy of Jacques ZS1PL's documentation of his 251 PSU.

Model 251 PSU (August 2015)

This one shows clear signs of a DPO

Said DPO fitted a second 2N3055 in parallel with the existing one. Parts of this job is nicely done, like the mounting of the heatsink and the two emittor resistors.

Other bits are just plain ugly, like this solder joint.

Also, he removed the over current SCR, and fitted that humungous 2N3670 16A SCR straight across the output -- proving that he doesn't understand the Ten-Tec SCR which shuts down the voltage regulator without popping any fuses. But he left the gate unconnected to anything but a pull-up resistor, so maybe he never finished the project. Who knows.

I first thought he might have added the second 2N3055 to spread the heat out a bit, but the shenanigans with the SCR proves that he was trying to get more current -- which is strange, because the transformer can only deliver what it's rated for. And in any case, it would have been a helluva lot simpler to just fit a 2N6258 transistor like the 252 PSU uses.

Anyway it's back to stock and back together now.

[Image] Hit Count hits since 2018-01-30.

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