[HAM] Recapping

[David Anderson]

Kai,

Actually, no TGs ever used any kind of (poly)styrene capacitor. That  
term was popularized by one big player in the Hammond business and,  
unfortunately, stuck for a while. It seems to be fading out of use.

The replacements for impregnated paper capacitors used a Mylar  
dielectric, the trade name for polyester film.

These Mylar capacitors were encased in plastic shells to protect them  
from moisture, and it was much more effective than wax-dipping,  
though the cost was that the heat needed to seal them in plastic  
damaged a percentage of capacitors in the manufacturing process.  
That's one reason they don't make them that way anymore.

Contrary to popular belief, Mylar capacitors are not immune to  
moisture. Mylar is half as absorptive of water as paper. The reason  
they don't suffer so much from drift is simply because they're better  
protected. I still have some plastic-encased paper capacitors in my  
1960 Scott integrated amp. I keep an eye on them for leakage, but  
they still work fine. The plastic shells protect them. (Polystyrene  
and polypropylene, on the other hand, are nearly impervious to water.)

During this period of the late 50s to the early 60s, you see both  
paper and Mylar capacitors in the same kind of plastic casings,  
making it difficult to tell sometimes what you're dealing with  
without cutting them open.

Polystyrene could never have been encased in plastic since its  
melting point is too low.

Use of Mylar capacitors on TGs started sometime in 1964 from what I  
know, prior to the addition of the RC high-pass filters.

What type of capacitor is it you've only seen on a 1937 organ? Can  
you send a photo of it?

David

On Mar 3, 2008, at 12:07 PM, kai lammervo wrote:

>       I saw lately a M3 with TG that had mostly those red styrene  
> caps, but also few older "cardboard" caps. I wonder how common this  
> is?
>
>   Last summer I was servicing an A-100 that had red styrene caps,  
> but no R/C networks! That was a 50hz unit, but the guy had also a  
> 60hz A-100 which had red styrene caps and no R/C networks either.  
> Amazing coincidence. Even if that wasn´t enough, they sounded like  
> night and day, totally different!
>
>   I´m assuming there might have been some period when there were  
> organs with earlier resonant circuits equipped with styrene caps,  
> and also later ones without R/C networks.
>   Thus far I have only seen these types of capacitors on a 1937 BC  
> organ ,
> but Scott has seen them on 1964 organs so therefore I suspect that
> Hammond used them indiscriminately depending on what batches were
> available at the time of their bulk purchase ordering from the various
> vendors.