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A Power Supply on the Cheap

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Need a variable power supply that is short circuit protected and over voltage protected; Here is a good one that can be built cheap.

Long time no see. You may remember me by the call VE3IVJ also now have VA3AQ. I have moved to Guelph and about 3 min walk to work. Also Sandy is about 2 min from work. Ron Reyn VE3IVJ/VA3AQ

Late one Saturday night I needed a variable DC supply that would supply about 6 amps and did not have one. Of course all the stores were closed. Out of a junk box I found all the parts I needed. The schematic here only shows the regulator circuit.

The transformer I pulled out of an old microwave and cut the high voltage side off with a hack saw (Carefully). I left the primary winding on and proceeded to wrap #12 gauge wire around the primary till I got about 18 volts AC and lots of current. I then sealed it with some 5 min epoxy.

I built the electronics on a small piece of copper coated perf board. I mounted 3 - 2n3055 transistors on a large heat sink I had lying around. I was able to run 10 amps and the supply was rock stable. The schematic only shows 2 pass transistors while I added 1 more. Had to heat sink the 2N2222 as well as it got a tad warm.

Think it could be built for about $10.00 not including the case. Well most of us hams don't put things in fancy cases anyways.

For the .1 ohm resistors I used a large paper clip wrapped around a 1/8th inch spindle.

73 Ron