[Arran]

I've noticed that the old cardboard tubular paper capacitors also often have a two digit number inside, usually on a piece of tape that sticks down the outside of the windings of paper and tin foil. Perhaps the number dictated the capacity in microfarads and the voltage of the capacitor before it was stuffed into its' shell, like a #30 would be a .05 uF 600 vdc unit and a #25 would be a .003 uf 400 vdc unit?
Speaking of tone correction capacitors, I have noticed that Philco had a preference in many of their sets for connecting such caps from the plate of the audio output tube to the cathode rather then between the plate and the screen grid. With such a setup they could get away with using a regular paper capacitor rather then having to use a 1 kv unit like some sets did.
Regards
Arran