• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

polystyrene capacitor

Status
Not open for further replies.

Pachinko7

New Member
A project I m trying to build calls for a 47p polystyrene capacitor. What are these ? I could not find it in a general catalog (Digi-Key). Can I use other kind of capacitor ? Thank you for your help.
 

Phasor

Member
For general purpose use, you should be ok with a ceramic capacitor - depends though, on the application - what is your project, and can you post a schematic?
 

TheOne

New Member
Polystyrene capacitors are noted for their low distortion, low dissipation factor, and excellent temperature stability. Typically used in equalization and tuner circuits
 

Pachinko7

New Member
Thank you. So I guess I will have to find the real thing ... :roll:
 

Pachinko7

New Member
Nigel Goodwin said:
Pachinko7 said:
Thank you. So I guess I will have to find the real thing ... :roll:
It depends on what it's used for, you still haven't mentioned that!.
Well, I am building the theremin project that appeared on EPE, October 2004, page 706. It should be cool... I am just trying to gather as many components as possible and start, I already prepared the PCB...
 

TheOne

New Member
Makes sense that you will want a stable capacitor for the oscillators.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Pachinko7 said:
Nigel Goodwin said:
Pachinko7 said:
Thank you. So I guess I will have to find the real thing ... :roll:
It depends on what it's used for, you still haven't mentioned that!.
Well, I am building the theremin project that appeared on EPE, October 2004, page 706. It should be cool... I am just trying to gather as many components as possible and start, I already prepared the PCB...
If you can find a silver-mica capacitor of the right value, they are even better than polystyrene.
 

Pachinko7

New Member
Nigel Goodwin said:
Pachinko7 said:
Nigel Goodwin said:
Pachinko7 said:
Thank you. So I guess I will have to find the real thing ... :roll:
It depends on what it's used for, you still haven't mentioned that!.
Well, I am building the theremin project that appeared on EPE, October 2004, page 706. It should be cool... I am just trying to gather as many components as possible and start, I already prepared the PCB...
If you can find a silver-mica capacitor of the right value, they are even better than polystyrene.
I found mica film capacitor of that value on Digi-Key catalogue. I does not mention anything about silver, though. (Part # 338-1017-ND). Is that the right kind of capacitor ?
 

TheOne

New Member
If your cap will be used in an oscillator, here are some facts to consider.
(This may not be critical to your application, but it is good to know)

Up to about 10MHz it is often practical to use polystyrene caps. They have a slight -ve temperature coefficient making them ideal to use with magnetic cores with a +ve coefficient.

Silver-mica can also be used but their individual drift characteristic may vary from -ve, zero or +ve (even for caps from the same batch!). The only way to grade them will be to monitor the capacitance with a cap meter for change in value over say a 1 hour period in a temperature chamber when the temperature is varied from about 50-100 deg F.

Once graded they make excellent capacitors for use in oscillators because of their high Q like polystyrene.
 

Pachinko7

New Member
TheOne said:
If your cap will be used in an oscillator, here are some facts to consider.
(This may not be critical to your application, but it is good to know)

Up to about 10MHz it is often practical to use polystyrene caps. They have a slight -ve temperature coefficient making them ideal to use with magnetic cores with a +ve coefficient.

Silver-mica can also be used but their individual drift characteristic may vary from -ve, zero or +ve (even for caps from the same batch!). The only way to grade them will be to monitor the capacitance with a cap meter for change in value over say a 1 hour period in a temperature chamber when the temperature is varied from about 50-100 deg F.

Once graded they make excellent capacitors for use in oscillators because of their high Q like polystyrene.
Thank you very much for this information. It makes sense to me that the characteristics of the silver-mica vary widely even for caps of the same batch, since the dielectric mica is a natural mineral, and is not produced under carefully controled conditions, like the man-made polymers (polystyrene, polyester, etc.). It is very likely that small impurities or variations in composition in the mica, even in the same specimen, will change its characteristics.
Why is the temperature coeficient called ve ?
 

TheOne

New Member
Pachinko7 said:
Why is the temperature coeficient called ve ?
It is just my shorthand way of saying positive (+ve) or negative (-ve)
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top