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Old 1st April 2003, 06:51 AM   #1
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Default Are these polyprop caps (pic)?

I have bought these parst surplus at Pollin.de, and according to their list they were MKP, i.e. metallized polypropylen foil. They don't look like one of the classic brands of polyprop caps like Siemens, Roederstein, Wima. I have seen similar devices on the servo board of a CDM4 Philips CD pickup, which would lead me to suspect they are ordinary MKP, i.e. polyester.

I am not sure about their construction, either. They are evidently rolled film, but the wires may be be stuck into the roll like older polystyrene caps, or they may be schooped to the sides.
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Old 1st April 2003, 06:52 AM   #2
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nt
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Old 1st April 2003, 07:05 AM   #3
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Lightbulb caps

Hi Eric,
These are ordinary MKT or polyester caps.
(Not polypropylene)
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Old 1st April 2003, 09:00 AM   #4
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Hi Elso,

do you happen to know the brand or have you ever bought them?

I have taken the 18 nF apart. It's a flat roll with the wires stuck into the middle. It contains a metal foil, so it would have to be FKT or FKP. The plastic foil is very thin, stiff and has a silverish sheen which may be residual aluminum or be due to the fact that it actually consists of at least three layers. I have no idea whether they rolled three foils on top of each other or whether the material simply splits like mica.

Is there a test for polyester vs. polyprop? I seem to remember that polyprop is dificult to glue.

Regards,

Eric
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Old 1st April 2003, 11:43 AM   #5
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Quote:
Originally posted by capslock
Is there a test for polyester vs. polyprop?
Some plastics when set alight can be identified by the colour of the flame and the particular smell. Should be easy to locate that kind of info.
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Old 1st April 2003, 12:49 PM   #6
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Have a look at http://www.madisound.com/sale.html

There are two caps the same color as mine. One is supposed to be polyprop, the other mylar (=polyester).
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Old 1st April 2003, 01:09 PM   #7
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Lightbulb Mylar or Polyprop?

Hi Eric,
Yes I admit it is confusing.
What you can do is, if you have available a capacitor tester, is this:
I take my daughters hairdryer and heat up the cap observing the meter.
Polyprop has a negative TC so the capacity decreases on heating.
Polyester or Mylar has a positive TC so the capacity increases on heating.
Polycarbonate has a small negative TC and remains fairly constant. Hope this helps!
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Old 1st April 2003, 01:37 PM   #8
Bricolo is offline Bricolo  France
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since you're talking about caps

can you explain me the difference between the different caps types? I've seen MKP, MKH, KP, and I don't know what this means, nor how good they are
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Old 1st April 2003, 02:19 PM   #9
tiroth is offline tiroth  United States
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That is good info Elso. Thanks!
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Old 1st April 2003, 02:25 PM   #10
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Quote:
Originally posted by Bricolo
since you're talking about caps

can you explain me the difference between the different caps types? I've seen MKP, MKH, KP, and I don't know what this means, nor how good they are
TC is temperature coefficient.

Read the following as an intro to caps for audio:

http://www.capacitors.com/pickcap/pickcap.htm

http://www.chipcenter.com/eexpert/ak...kruger017.html

http://www.evox-rifa.com/cap_catalog/p4-2/geninfor.pdf
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