OK, you guys will get a kick out of this. Per Randall's suggestion, I went on the internet and bought a growler for $35. Now, don't laugh, cause the one that was ending the auction first is a 90 year old Growler!
Is that cool or what!?! As usual, I studied the deal for three days and realized the principal is simple, and the newer ones only differ in that most have a built in volt/ammeter. The physics are that the device is just an open core electro-magnet. It is wound with a 110 volt coil, and the armature is placed on the open end to close the core. Here are the basics of how easy it works...
The armature is placed on the growler as in the first pic, and the power for the 110v coil is switched on. This starts to cycle a 60hz pulsing magnetic field around the armature, and the steel in the armature completes the growler core. Now, you take something with iron, in my case a hack-saw blade, and spin the armature as you hold the blade over the top. If the windings in the armature are intact, the blade is just lightly magnetically attracted to the armature, since the field generated by the windings offset the growler magnetic field. If there are any shorts in the armature winding, the blade will rattle on the armature at 60 hz, in the region with the shorted winding. I don't understand...but apparently the shorted winding is unable to offset the growler field. That insures that the armature has no shorts in the coils.
Step 2. Here you use these contactors to check each adjacent set of contacts on the commutator. The growler power is off for this. If there is an open coil, the light will not light as you check 2 adjacent. The armature I broke had 2 open wires, and sure enough, the light test failed at 2 locations on the commutator.
Step 3. Now use the light contactors to check the commutator to the armature core. You can check each commutator contact, but if the other checks were good, any contact will light the light if there is a short to the core.
Step 4. Here we switch on the growler again and use a voltmeter. Those new-fangled growlers have the volt meter built in...I had to use a separate one. Now, you test the voltage that the growler magnetic field is inducing within the armature. Viewed from the commutator end of my pic, the highest induced voltage is at the 9 o-clock position. Once again, you check 2 adjacent commutator pads. This particular armature produced 1.4 volts. Now rotate the armature one pad and check the next two contacts for the same 1.4 volts at the same 9 o-clock position...and so on till you are around the entire commutator. You have just made sure that none of the coils in the armature have partial internal shorts within the coils.
That's it!
I checked 5 generator and 1 starter armature in about 30 minutes. And, best of all, I have a working antique "Growler" to hang on the office wall now!