Hickok Model 370 Auto Polarity FET Multimeter

I'm a sucker for a big, easy to read, mirrored analog meter movement, and I just couldn't resist picking up this 1970's Hickok 370 when I came across it. It has a 6" meter movement and is basically a solid state version of a vacuum tube voltmeter (VTVM).
It's an auto-polarity meter which is not something I normally see on an analog meter. The rest of its specs are decent too, as can be seen in the photo, so it will be a useful meter around the lab, even if I didn't really need another one.

The meter uses standard test leads which is both good and bad. It's good not needing special probes, but the simple leads pick up noise on the high ohms ranges causing the meter to bob around.
The instruction manual explains how to make measurements on these scales. I use a shielded coaxial test lead which minimizes the noise pickup, but doesn't entirely eliminate it.

Calibrating the meter is pretty simple with just one pot for adjusting DCV, a trimmer cap for ACV, and a pot to align the Hi Ω range.
The blue and black cabinet has aluminum panels with a textured vinyl covering. The front panel had some small scratches and pencil marks, and someone sloppily scratched initials into it under the meter movement. Kind of juvenile looking which makes me think this meter probably came from a school, and I think that's likely the market this meter was designed for. I cleaned off all the penciling and put a "Meter Zero" label over the initial scratches just to hide them. Also, one of the knobs is missing a bright, so I'll have to see if I can find a replacement.
The PCB is in good shape and it doesn't look like anyone has worked on it. Two traces running under the power supply filter capacitor were a bit corroded and were cleaned up when the cap was replaced.

The Ohms function was pegging the meter and I had to clean the "Ω Adj" pot to fix it. I also cleaned the "Zero Adj" pot and all the pushbutton switches while I was at it. Every range works now.
The only two parts replaced were the power supply filter cap and the electrolytic across the meter terminals.

An operating manual with calibration instructions, a parts list, and a schematic is available for download on the BAMA manual website.
This meter was in good condition as received so it took less than a day to clean, test, troubleshoot and calibrate.
Page created 6/4/2023
Last edited 7/21/2023