Polyester vs. polystyrene

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frogmasked

New Member

• Oct 6, 2008

• #1

Hi guys,
I'm new to electronics, I'm building a synth project and I need
to know if what's supposed to be a polystyrene cap can be replaced by
a polyester cap. Can anybody help?

Thanks in advance.

 

RadioRon

Well-Known Member

• Oct 6, 2008

• #2

I believe that you can make this change without much concern. Both technologies are very stable vs temperature which is probably your main priority. There may be differences in breakdown voltage behavior or other characteristic, but I've done this substitution and had no problems.

 

F

frogmasked

New Member

• Oct 6, 2008

• #3

Thank you so much for your quick, helpful reply.
I will try this out.

 

S

Speakerguy

Active Member

• Oct 6, 2008

• #4

Yes, a polyester cap should be fine.

 

D

Dean Huster

Well-Known Member

• Oct 6, 2008

• #5

Besides, polyester (aka Mylar, a DuPont tradename) caps are easier to find in catalogs. Polystyrene caps tend to have lower values overall, in the tens and hundreds of picofarads where the polyester caps are available in higher values, 1 nF (.001 µF) through .47µF (470 nF).

Dean

 

Hero999

Banned

• Oct 7, 2008

• #6

The thing I like about polystyrene is they're very close tollerance, typically <5% and I've seen 1% before, which is great for building filters.

 

D

Dean Huster

Well-Known Member

• Oct 7, 2008

• #7

I tend to agree, but I've seen plenty of Mylars with 1% tolerance, also. They tend to be found more in the "surplus" electronics catalogs.

Dean

 

Last edited: Oct 7, 2008

Roff

Well-Known Member

• Oct 7, 2008

• #8

IIRC, polystyrene melts at about 240C, so soldering requires some care. It has very low dielectric absorption, making it especially desirable in sample-and-hold circuits.

 

S

Speakerguy

Active Member

• Oct 7, 2008

• #9

Polypropylene are easy to find in 1% but they cost significantly more than your standard 5% mylar.

 

D

Dean Huster

Well-Known Member

• Oct 9, 2008

• #10

Ooooh, that's right, Ron/Roff! It's amazing the number of late-1960s-era kits with melted polystyrene caps. They used to use a lot of them back then in solid-state receiver circuits when kit builders were still soldering PCBs as though they were working with terminal strips and tube sockets!

Dean