"non-polar" capacitor?

[Chuck Guzis]

On 07/30/2016 10:24 PM, Jim Brain wrote:
> Since I acquired a Coco Orchestra 90 unit awhile back, and I am
> trying to find the source of some humming in my system when the Orch
> 90 unit is operational, I looked at the schematic:
> 
> 
> http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Orchestra-90%20CC%20Stereo%20Music%20Synthesizer%20(Tandy).pdf
>
> 
> 

> Can someone shed light on what these are and where you would find
> them (or if they can safely be replaced with another kind of
> capacitor)?  I will admit I've never seen mention of these before
> now.
> 

Electrolytic caps have different characteristics (they actually act
somewhat akin to diodes) in the reverse direction.  Often, what's done
is to construct a non-polar cap by taking two capacitors of double the
capacitance in series with like poles forming the connection.   You can
also run into nonpolar caps used in AC power circuits as PF adjustment,
motor starting/run etc. with special construction (i.e. oil dielectric).

However, the small values that I see in the schematic would seem to
suggest that plain old film caps (polyester/polypropylene)  will do the
job just fine.

FWIW,
--Chuck