On Nov 4, 11:32*pm, Bill Baka wrote:
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

Two comments...
Bill, good luck with the radio project. I have an old cap checker
with eye tube (in virtually new condition) but find it of little use,
rather it's just a curiosity. A DVM (use your Fluke 77) and a
variable B+ voltage source is much more useful. A Q&D check on
coupling caps is to measure the voltage on the following g1 - anything
over +2 mV to ground is suspect. But don't bother to check the wax
caps, just replace them all - electrolytics, too.

An earlier post suggested I replace the risky brown 0.1 uF caps in the
Bendix RA 10DB receiver if their failure could take out an original
IFT. As far as I can see, no shorted decoupling cap can take out any
IFT since they are all above the IFT's. But, if they fail, they will
take out the 1Kohm decoupling resistor and stress the dynamotor so, as
I said, all the ones with B+ on them will be replaced.
Cheers,
Roger