Right Hand of Zod: Slice of Schlumberger..

NOTE FROM THE FUTURE: With the greatest respect to the Swedish gentleman who firsty proposed and did this to his Schlumberger, this mod sucks. I restored this beautiful instrument to its original condition and moved on. Everything is so-o-o-o much happier in my world now. Also, I am over the VTVM jones at this point, retraining two of the four or five that I had. I believe it to be this and a fully-restored, pristine V-7A that adorns my bench.

Not all of the VTVMs I stumbled onto were dogs or fraught with problems. In fact, I should have quit winners. My friend Lloyd said he had a Heath-Schlumberger SM-20 he wanted to part with and I picked it up from him for $15. it was a little dinged on the outside (what sixties vintage meter isn't) but a little TLC and a nick of paint brought it back to its former glory.(Heath-Schlumberger was the commercial side of Heathkit and these were usually the pre- or commercially-built kits that you found at trade schools, etc. This one had those stenciled markings on the case before it was repainted.

Turned out to be reasonably accurate also -- after I exorcised the demons with some contact cleaner and a few joint re-melts.

Like a lot of Heathkits and VTVMs of that era, it had that single stereo phone jack for its test leads. In this case, the probe served a dual purpose (see schematic snippet below) and was switchable between AC Volts+Ohms to DC Volts. Of course, the probes and leads have gone by the boards and it will require some art to reconstruct them. Heath buried a 1-megohm resistor in the probe to isolate it from DC pickup. (I am still trying to get my head around that one.)

In any event, since there were no probes, I regrettably did some cosmetic surgery on the box and made it usable with standard banana jack leads. I got the idea from a very nice Swedish ham, Hans Gatu, who has quite a collection of Heathkits and tends to make this mod on all of his older VTVMs.

Hans wrote me and explained that he found not a lot of problems putting the extra 1-megohm resistor inside the unit and it was a decent trade-off for being able to use conventional cables and test leads. As my pictures show, I mimicked Hans quite closely.