2021-07-29 Heathkit IP-18 Power Supply Re-Cap

Last week I saw an old Heathkit IP-18 power supply on eBay for $50 OBO, free shipping. I don’t really need another PS, but I’m a Heathkit builder and a big fan. So I offered $30, thinking the seller would not take it. But a few hours later the message came that the seller had accepted the offer. So today it arrived on my doorstep.

It puts out 1 to 15 volts at up to 1/2 amp. The current pot allows it to limit the current to as low as 10 mA according to the specifications.

I didn’t bother plugging it in; I opened it up to see if it was assembled properly. I was relieved to see it was okay. But the main filter capacitor had grunge out of the end, so I unsoldered it and found it was only a thousand picofarads instead of 2500 microfarads – completely open. So I found a couple capacitors to put in parallel to give about the same capacitance — the old cap was the size of a C cell so there was plenty of room.

I didn’t see any grunge on the others so plugged it in and put a DMM and load resistor on it to see how it worked. Well, it worked so-so — the regulation wasn’t very good. So I unplugged it and pulled other electrolytic capacitors and measured them and found they, too, only measured a few thousand picofarads. So I scrounged around for some decent substitute capacitors and got them soldered in.

After that, I hooked it up with the DMM and load resistor, and wow! The fresh capacitors made a real difference. The old timer is barely noticing when I turn it to 10 V and put a 30 ohm load on it — the voltage barely changes. The regulation is now very good with 1/3 amp load. And the current control allows it to be adjusted down. It’s as good as new! 😉

The one thing it lacks is a meter for adjusting the voltage. But I have a cheap, tiny DMM PCB that runs on 4 to 15 volts. I’ll glue it to the front panel. 👍👍

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