PA4TIM, I like your site also. I have the Tektronix TM-504 on my bench also with the following plug-ins: function generator, DMM, Counter, and dual power supply. On of these days I'd like to find the oscilloscope plug-in for it. Don't need it but I would like to see how well it works.
Here's the info on the 650A: Made around 1940. Pretty much a fixed voltage around 45 V for testing and variable for leakage tests.
USAGE NOTES
· The "test voltage" control knob only applies to leakage tests. All capacitance
tests are done at around 45 volts a.c. combined with just over 10 volts d.c., so
don't test any capacitor on your 650A that's not rated for 50 or more volts.
· On paper/mica leakage tests, it takes 3 microamps of leakage to keep the eye
tube from fully opening (~40 megohms of insulation resistance). If leakage is
under 3 microamps, the eye tube will open fully.
· For electrolytic leakage tests, 0.5 milliamps is the leakage threshold at which the
eye tube will open.
· The power factor control only applies to the CH and C1 ranges.
· When all buttons are released (out), any capacitor attached to the terminals
discharges through a 200 ohm resistor. Let any capacitor you test discharge
before removing it, and make sure the buttons are fully released. Any button
being pressed or stuck in even by a small amount will keep the discharge circuit
from being completed, so be aware of potential voltages on your cap's if your
buttons don't release fully.
· The higher the value and higher the voltage used for leakage tests, the longer it
will take for the eye tube to open. Be patient with large caps, it can take a few
seconds.
I actually use a Sprague TO-5 on my bench.