Heathkit MP-10 power inverter

[DavePEI]

This isn't really a Telephone tool, but is a vintage tool which can help out anyone who needs a 120 volt AC power source in a vehicle. Sure, there are more modern versions available, but I thought it was neat to be able to bring this back to life on a rainy day!

This morning's project (remotely associated with the LIU), was repairing a Heathkit MP-10 power inverter I bought in a yard sale years ago for $1. This will take 6 or 12 volts and convert it to 120 VAC (square wave) with 175 watts  (240 watt intermittent) output when running from 12 VDC -   enough to power an electric drill, electric light, etc. Output wattage is some-what lower (120 watt) when running from a 6 VDC source.

At any rate, it never did work, but it got placed on the indefinite "don't want to throw it out yet" pile. Well, I decided if I wanted to fix it up, it would be ideal;  though a bit recent to keep in the LIU. I had never bothered with it, as I suspected the problem, aside from a bad fuse holder, was one or both of the switching transistors had failed.

As I got into it, I discovered that is wasn't one of the hard to get germanium transistors gone, it was a shorted 5uf capacitor across the output of the multi-vibrator.

Had it been one or both of the transistors, that would have been a problem, as the original Motorola made Heath 417-60s (Germanium PNP 45 V,  25 A ,100 W in a TO-3 case) haven't been made for many years, and today's closest equivalent is the DTG110B costing about $35 ea. (approximately what the entire unit would have cost in the 60s).

So, I replaced the capacitor and the bad fuse holder, cleaned it up, and despite the fact it was built  in 1965, and is now 50 years old, it works as well as it was designed to back then... To think I had left it on the side-burner for at least 10 years!

Thursday a.m., I replaced the light 12 volt wires on it with 10 gauge wires. While the light gauge wires on it originally would do for small loads, it needs to have much heavier wire to connect it to the battery of the vehicle, the specs calling for at least 10 gauge and no longer than ten feet long. I am sure that with even heavier gauge wire, the distance from the battery could be increased.

I love all vintage stuff!

A video showing this unit (not mine): https://www.youtube.com/watch?v=GVX34k9ljU4

Dave