Posting again since I do not see my initial posting.
Looking for a copy of simple plans to build a growler armiture tester. I have the coil but want to add light and switch.
The light does not come into play when using the growler. The light is used like a meter to check for shorts and open circuits in the windings and armature. The one on mine runs 120 V through the light bulb to do the checking. I would suggest just using an analog meter to do the same job and the growler for checking for shorts in the windings. You only need to have an on/off switch to the growler.
Mark is correct.
As you know growlers with the hacksaw blade tests for inter-winding shorts.
The test probes and low wattage bulb feature for checking continuity are a safety hazard. OSHA would have never allowed them to use that feature if it were made/sold today. You can do a better job with a ohmmeter to check for grounded windings (they are all in series).
Some growlers have a third feature; Two probes that place a current with a meter in series and you can place these probes on adjacent commutator bars and read the current flow in each winding. That check will help you find intra-winding shorts by comparing each windings current draw.
You can commonly find growlers with two or three of these features on eBay very cheaply. Few people use this kind of tool today.
Here is a photo of my growler with all three features.
Ron the Coilman
Hey Ron, how'd you get my growler out of my shop without me noticing? JK, I have the exact same model. It's reassuring to know that I stumbled onto the tool the the expert uses.
It's pretty hard (read impossible) to test for an open armature coil segment with an ohm meter. The winding is called a "series wave" but the coils are actually connected in parallel 1. Since all the coils are connected together, about all you can do is check to see if there's a short to ground. But even that is not very reliable. The short may not occur until the armature is spinning or under a load. That's where the light can help. I've had armatures let out their "good smoke" testing with a light that otherwise passed the no-ground and growler test. I don't even bother with the tests on old windings any more. I just replace them.
Keep in mind that the windings on these armatures are 83-91 years old and subject to the worst environment possible. Not to mention rotting insulation. You might get away with re-using a starter armature but if you're doing a rebuild on a generator, rebuild it! Other than replacing brushes and an occasional cleaning, It will probably out last you.
1 (Because the winding progresses in one direction around the armature in a series of 'waves' it is know as wave winding.)
Thanks to all who answered. I have a better idea now on how to proceed. Ron F