On Sunday, 12 November 2017 05:42:41 UTC, wrote:

I have an old radio that has a "domino cap" between the plate and
cathode of a 50B5 audio output tube. The dots were never colored on it.
It appears to be a Micamold brand (hard to read). It has 3 uncolored
dots between arrows, and one more dot above them.

Instead of coloring the dots, there is this [ CA-281 ] stamped on it.
Does that mean anything? Or is that a manufacturer part #?

to micamold it probably did. Probably is.

The schematic says it's supposed to be a .01uf @ 600v.
This is a Abbotwares Z477 radio from 1947.

Normally I dont even bother with those mica caps, since they do not
normally go bad. However, this radio had one lead to that cap cut, so
there is likely a problem with it. (Maybe)??? (or it was worked on by
someone who dont know much)...

After I replace the nasty looking filter cap and a few other caps that
look very bad, I will plug it in. Then I will clip this cap back into
the circuit and see if it really is bad or not....

Anyhow, if I want to replace it, what is the best replacement. Can I use
a ceramic disk, or should I try to locate a mica (probably wont be easy
to find), or just use a modern tubular cap rated at 600v?

Mica had low ESL and high stability.

The old one is reading 9.73 NF with my meter, so that is close to the
correct amount. (Of course there is no voltage on it, so it make
breakdown when voltage is applied).

Why not test it, easy enough to do. Mains & a small mains LED in series would test it to 330v in 240v land.


NT