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Electronics => Repair => Topic started by: basinstreetdesign on February 23, 2019, 07:45:00 pm

Title: Where can I get Triplett VOM model 1200-F data?
Post by: basinstreetdesign on February 23, 2019, 07:45:00 pm
I've finally taken a meter I've had for several years off the shelf to see if I could fix and calibrate it. I would like it to be just as good as new again.  :-DMM
It's a Triplett VOM model 1200-F in pretty good shape except for a lack of a battery box, a busted pin jack and a sticky push-button switch. I have Googled several times but can find nothing on this instrument. Does anybody know where I can get a schematic or specs on it?
Thanks in advance, Tim.
Title: Re: Where can I get Triplett VOM model 1200-F data?
Post by: barry14 on February 23, 2019, 09:18:02 pm
Some information can be found at the following site: (
Title: Re: Where can I get Triplett VOM model 1200-F data?
Post by: basinstreetdesign on May 05, 2019, 12:16:41 am
In searching for info on this V-O-M I found close to the square root of zip except for the photo in the radiomuseum listing.  And I already knew what it looked like (1st shot below).  Inside were a bunch of wildely out-of-spec resistors, a kaput cap, two shot Ohms cal pots and no battery compartment, a broken connector and no known schematic (2nd, 3rd, 4th shots).

So I decided to re-wire it.  I followed the original philosophy as much as I could but some parts were just a mystery.  Such as why was the 1K Ohms range marked backwards from the other 3 Ohms ranges, what was I going to do about a strange broken pin jack that connected two wires only when a pin plug was plugged into it?  Since I didn't have any pin plugs that I could use on the unit anyway and I wanted to use just parts I had and didn't want to spend money on it, I decided to re-fit it with banana terminals and replace the R's, the C.

Since it would never be used elsewhere than my bench and I wanted to avoid putting new (and possibly unobtainium) batteries into it forever, I built a small multi-voltage power supply that would be supplied from a wall wart from my glory box of wall warts.  (I love when the use of some wall wart can be justified.)  All of the three Ohms pots came from my collection.  Two are mil-spec.  A good deal of mathematical analysis went into choosing the right voltages and resistor/pot values to power the Ohms scales.  The three upper Ohms ranges operate the usual way with the unknown in series with the voltage source and the meter, but the LO Ohms range, 0-1K operates with the unknown in parallel with the meter.  Thus zero for it is NEAR the left end of the scale whereas the others have zero at the right end of the scale.

Calibration certainly cannot match current day meters.  With zero voltages and FSD voltage calibrated at the ends of the scale, the mid points are always out of calibration by up to 5%.  Ohms is even worse than that near the high-value end, of course, but the zero end can always be calibrated.

I will probably use it only for VDC or VAC monitoring of some non-critical voltage in a project but it still serves to give me another voltmeter so that my more accurate ones needn't be used up with that.

So I hope I didn't disgust anybody by adulterating a venerated meter, not trying to restore it to pristine original factory-fresh condition.  I wasn't about to go those lengths but I wanted to restore the function of this nice 80+ year-old meter to useful status.