Engineer wrote:

Thanks, Bill. I've used these rectagular black plastic 0.12 (and
0.18) caps for a while now as coupling caps in various amplifiers and
radios with no problems - virtually zero mV positive voltages measured
on any g1's. I have a bag of each, acquired from a retired EE and
radio hobbyist. Also used them for RF decoupling in radios, again no
problems.
Cheers,
Roger

Roger,
I have an old Echophone on my computer desk right now and the bottom is
missing as well as the back. It has normal round resistors, octal tubes,
and 5 wax covered paper caps. There are other caps that look near the
same but no wax on them. Could be the wax oozes out after 60 years or
so. There is a foil .25uF @ 200V and 2 electrolytics at 80 uF @ 150VDC
and a 30uF @ 150VDC.
I have a Heathkit cap checker and a Fluke 77 for checking the resistors
so next comes the fire up and check for noise. It isn't, as I always
say, rocket science, but a fair amount of work.
Of course a schematic would have been nice but I think I can trace it
out with not too much problem. There is a cap dangling but I think I
know where it goes.
My new, small project.
Thanks for listening.
Bill Baka