Has anyone seen these two types of capacitors? - Page 1
Forum section: electronics / beginners

author: RonFred2
author_rank: Contributor
timestamp: September 27, 2018, 03:35:22 am
content: While sorting a box full of parts from the 1980's I found two capacitor types I have never seen before:Glass bead looking thing measuring 1.5 nF (see photo)Tubular looking thing with outer coating like ceramic measuring 150 pF (see photo)Can someone tell me what type of capacitor they are and best usage in design/circuit? Also do you think these caps are still good after 35+ years?

author: ArthurDent
author_rank: Super Contributor
timestamp: September 27, 2018, 03:51:41 am
content: Here you go.

author: ataradov
author_rank: Super Contributor
timestamp: September 27, 2018, 03:53:27 am
content: The transparent one is a polystyrene film capacitor. They do age due to plastic shrinking, but it is still probably fine.Tubular one is old-timey ceramic capacitor. Probably also works. But there is no real point in using either of them nowadays.

author: floobydust
author_rank: Super Contributor
timestamp: September 27, 2018, 03:57:39 am
content: The 152J is a polystyrene film capacitor 1,500pF 5%. Xicon manufactures them, available at Mouser.They are for applications needing low dielectric absorption, and audio filters, timing use. Not so popular today because they are large size.The tubular or "dog bone capacitor", usually have a large temperature coefficient to correct RF circuits over temperature. They were popular in Tektronix scopes through the 1980's.

author: Benta
author_rank: Super Contributor
timestamp: September 27, 2018, 04:24:55 pm
content: From what I've heard, polystyrene caps are no longer produced, as polystyrene film has been phased out. Replacement is polypropylene.

author: chris_leyson
author_rank: Super Contributor
timestamp: September 27, 2018, 05:06:02 pm
content: That radial leaded polystyrene cap is not as common as as the axial variety.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 27, 2018, 05:21:16 pm
content: Quote from: Benta on September 27, 2018, 04:24:55 pmThat is correct. There was an article in one of the trade magazines, which indicated that the world's remaining polystyrene film factory had shut down.That there were plenty of virgin film stock available, but that eventually, it would run out.That article appeared perhaps 4 years ago...

author: drussell
author_rank: Super Contributor
timestamp: September 27, 2018, 05:48:10 pm
content: Quote from: floobydust on September 27, 2018, 03:57:39 amThey were available in a variety of temperature coefficients, including 0.

author: Zero999
author_rank: Super Contributor
timestamp: September 27, 2018, 07:44:45 pm
content: Quote from: schmitt trigger on September 27, 2018, 05:21:16 pmI believe the main reason polystyrene is no longer used for capacitors because poorer resistance to solvents, than polypropylene.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 27, 2018, 08:08:38 pm
content: It was a very good dielectric, though.I had once a PLL circuit with excessive jitter. I could not figure out why.A personal anecdote: Out of sheer desperation, I replaced the loop filter's capacitor from a NPO ceramic to a polystyrene type.The jitter diminished significantly.One unknown fact about polysterene caps is that they have what appears to be a "polarity" band.It is not actual polarity, but indicates which terminal is connected to the outermost foil.You should connect that terminal to the closest potential to ground. Or in the case of my example, where one capacitor end is grounded, to ground.That eliminates noise pickup in sensitive nodes.

author: floobydust
author_rank: Super Contributor
timestamp: September 27, 2018, 08:24:49 pm
content: Polystyrene are still in production, I get axial and radial Xicon parts from Mouser up to 10nF.I still buy/use polystyrene for A/D integrator caps and high-end audio use, as only Teflon is a better dielectric. Once you use a few in an application where the dielectric's properties are important, then you easily see the differences.The package melts easily and reflow is not the greatest for it, and it has relatively high self-inductance being a physically large part.