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 Polarized vs. non-polarized caps...

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Aaron

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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 4:33 pm

Lou deGonzague wrote:
There is no doubt that a mylar film cap will outlast any electrolytic under normal conditions used in a radio. I have nos electrolytics from the 30's and they are all bad. Also electrolytics do explode sometimes when they go bad. Using a mylar in place of a small electrolytic is a good idea especially in the old AK's and others that used 1 or 2 mfd in their powerpacks.

Since I'm the one who started this discussion, I thought I'd report back. I used a 2.2 uF mylar cap in place of a 2 uF electrolytic in an early '50s RCA am/fm set that I'm working on for a friend. It worked just fine. Smile

I like using a mylar cap in place of a small-value e-cap because it's hard to find 1 and 2 uF e-caps with axial leads.

Aaron
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 5:26 pm

Everything 5uf or under I use polyfilm.
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Mike W.

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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 6:57 pm

So, polarization aside... I' d thought that if it's an E-cap, then it's an E-cap for a reason. Like E-caps have a certain amount of leakage that is called for in a circuit where a paper/film cap does not. So it's safe to say I thought wrong, and if the voltage/capacitance is the same, a film cap CAN replace an E-cap? And for that matter any capacitor can replace any capacitor, film/disc/electrolytic/whatever? Cost and size aside, capacitance/voltage is capacitance/voltage regardless?
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 7:02 pm

Mike W. wrote:
So, polarization aside... I' d thought that if it's an E-cap, then it's an E-cap for a reason. Like E-caps have a certain amount of leakage that is called for in a circuit where a paper/film cap does not. So it's safe to say I thought wrong, and if the voltage/capacitance is the same, a film cap CAN replace an E-cap? And for that matter any capacitor can replace any capacitor, film/disc/electrolytic/whatever? Cost and size aside, capacitance/voltage is capacitance/voltage regardless?
Electrolytics should not be used in place of an electrostatic type.
Higher leakage current, polarization and higher esr.
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jack shirley



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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 8:24 pm

Mike W. wrote:
So, polarization aside... I' d thought that if it's an E-cap, then it's an E-cap for a reason. Like E-caps have a certain amount of leakage that is called for in a circuit where a paper/film cap does not. So it's safe to say I thought wrong, and if the voltage/capacitance is the same, a film cap CAN replace an E-cap? And for that matter any capacitor can replace any capacitor, film/disc/electrolytic/whatever? Cost and size aside, capacitance/voltage is capacitance/voltage regardless?

Your final statements are basically true. You're not going to find a .001 mica ceramic disc paper electrolytic so the field thins out rapidly. )P

There's no inherent "leakage" or the like figured into an electrolytic cap.

Well, since threads like this often go into obscure detailla to make a point...some of the old 30s radios counted on the PS filter cap for B+ bypassing at audio frequencies. This wasn't always effective. RCA often added a smaller cap of 0.1 or 0.25 across the large electrolytic for better bypassing at frequencies higher than the typical 60/120 cycles from the power supply. Philco came up with those coil-around-a-cap to divert similar issues of poor bypassing.

The electronic theory is valid in all such cases but the application varies greatly. That's not "in the book".

Back to your question, though. There's no 'magic' associated with electrolytic capacitors. They are just cheaper/smaller/less expensive to produce.

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pixellany



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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 10:10 pm

"A capacitor is a capacitor"

One of the reasons this in not true is that the equivalent circuit varies widely depending on the physical size and shape, the choice of dielectric, etc. Some capacitors have a relatively high ESR (equivalent series resistance), and ALL capacitors start looking more like inductors when the frequency is high enough (this depends primarily on the size and shape.)

The actual usage in a circuit defines how much you need to be worried about these "features".
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radiorich



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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 11:32 pm

Hello guys,
I have to agree with Carl on this on .

Rich
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