Please forgive me but I thought it interesting... Today I opened up three coils to replace the capacitors and two of them had capacitors that were about the size and shape of a AAA battery. All I had seen were the oval shaped rolled up foil.
Someone has been their before you.
Unless they are the light weight wood JC Whitney coils marked KW with rough unstained wood.
Don't know what is in those.
But they usually had good points to rob off 'em.
I'm guessing they had cores made of stacks of flat sheet metal rather than a bundle of round iron wires?
New one on me. After after market as Jim suggests?
I only dug out enough tar to expose the capacitors but the lumps on the other side look the same as the ones with the rolled foil capacitors.
The core is a bundle of iron wires.The top of which protrudes out the top of the coil,under the vibrator.
most are a bundle of wires...some of the KW's (I think KW's...maybe JC Whitney??) built in the 60's-70's had a number of flat plates, sort of like a bunch of small engineer's rulers stacked up and wound around
Those flat metal cored KW's usually measure almost 10,000 ohms for the secondary since the wire is super thin. I don't use those windings at all in my new box coils because I think they are kinda frail but they do seem to run OK if you change their usual .18uF capacitor to the "standard" .47uF and make sure that the capacitor dV/dT rating is high. The new flat oval ones have a dV/dT rating around 1700 Volts/uS which is more than double what they have to be to work in the T coil. The coil will run just fine with the .18uF capacitor they come with but the point life would be shorter since there is more arcing at the points. Most of those coils that I have run across have the box still in good shape so I don't do anything to them other than pass them to someone who wants them and will put new points on them and install a correct capacitor.