Bill,
When testing caps I use a digital meter to get a “face value” The Merc O T gives load testing value. Now lets look at design date from the 50’s. What is drifting from “new” values with the MOT meter? What you are testing is the dielectrics of the cap. It was rated at a given value when new. Elapsed time of testing should be finite, reflection of run time. I don’t have my manual in front of me but all resistance test will look for flaky or open conditions. We had Vitals monitors in I.C.U. in the hospital that would go flaky because the sheets lint made semi conductors & changes values. A blow out with Med air fixed them. Contamination with the MOT & environment contaminates both. I would tap on the component while testing. & remember design is from the 50’s. How long has it been since the machine has been calibrated too? I tinker with electronics & any data on the MOT is very protected + manufactures of these have components “built to value” a run of say 10, 000 & then there’s no more to replace.
A cap is rolled up foill, insulator (waxed paper) & foil encased. Easy to get shrinkage, deformation & leakage + failure intermittent values. Check at different temps ( ice pack & hair dryer) to evaluate, not too hot but mtr temps anyway.
The vibrator which outputs Pulsed D.C. for coil testing has a frequency it pulses at to charge/ discharge the coil for testing to simulate points opening/ closing & the frequency should be around say 5000 refering to engine RPM & I’m sure an electro-mechanical devise is not stable. Looked in to it years ago & even a heavy duty switching like a darlington transistor was hard to find. The early auto radio has a vibrator to make a pulsed signal to input a small transformer (coil) to up the voltage, inverter to run the tubes in the reciever.
Coils are transformers on induced from magnetic flux not an direct AC voltage not inclusive of early battery fed type outboards.
P.S. I researched cays from Vishay man. & the rep advised voltage rating @ 800 or above for Mags.
