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silver mica or polystyrene
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Old 6th February 2003, 02:01 PM   #1
janey is offline janey
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Default silver mica or polystyrene

silver mica or polystyrene ???

Which one for 10pF cap in Alephs.

janey
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Old 6th February 2003, 02:26 PM   #2
fmak is offline fmak
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Default Re: silver mica or polystyrene

Quote:
Originally posted by janey
silver mica or polystyrene ???

Which one for 10pF cap in Alephs.

janey
----------------------------------

Definitely Ps, if not too warm.
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Old 6th February 2003, 04:27 PM   #3
Bobken is offline Bobken  United Kingdom
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Hi,

*Extended foil* polystyrenes, and the better non-magnetic leaded Sil micas, are both very good sonically. After many comparisons in a lot of different areas, I have found it hard to come to any overall conclusion.

Both seem to have their merits, and in some locations, one seems preferable to me, and in alternative locations, I marginally prefer the other.

Regards,
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Old 6th February 2003, 08:41 PM   #4
Nelson Pass is offline Nelson Pass  United States
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silver mica or polystyrene
For 10 pF, the best is wire-wrap wire, two pieces
twisted together. Cut to desired value of pF
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Old 6th February 2003, 08:54 PM   #5
Christer is offline Christer  Sweden
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Quote:
Originally posted by Nelson Pass
For 10 pF, the best is wire-wrap wire, two pieces
twisted together. Cut to desired value of pF

That was a new one. Sounds a reasonable thing to do, and I
am sure it is since you recommend it, but won't you get
problems with inductance?
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Old 6th February 2003, 08:55 PM   #6
Netlist is offline Netlist  Belgium
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That's real DIY!!

One day I'll make my own resistors from old Belgium money.

But when we buy 10pF, we now it's +/- 10pF.
When we try to make it with wire wrap it's hard to measure.
Even with a good DMM as a Fluke and original Fluke leads the tolerance of the meter and leads vary too much to measure 10pF not to speak about 5pF.

Or is there a better way to perform a correct measure?

/Hugo - always has problems with meter tolerances...
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Old 6th February 2003, 09:07 PM   #7
Christer is offline Christer  Sweden
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Quote:
Originally posted by Netlist
That's real DIY!!

One day I'll make my own resistors from old Belgium money.
Well, I am not sure about resistors, but my father used to
make capacitors from the metal foil wrapped around chocolate.


Quote:

But when we buy 10pF, we now it's +/- 10pF.
When we try to make it with wire wrap it's hard to measure.
Even with a good DMM as a Fluke and original Fluke leads the tolerance of the meter and leads vary too much to measure 10pF not to speak about 5pF.

Or is there a better way to perform a correct measure?

/Hugo - always has problems with meter tolerances...
I suppose you mean +/- 10%? I wouldn't like to buy a cap
that has +/- 100% tolerance.

Anyway, I think the best way is not to measure, but try to
calculate the required wire length. I don't remember the
formula for capacitance between wires, but it shouldn't be
too hard to find in some book, or on the net. You also need
to know the wire diameter, insulation thickness and the
dielectricity constant for the insulation, but I would guess that
you can get a pretty good accuracy this way.
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Old 6th February 2003, 09:10 PM   #8
Nelson Pass is offline Nelson Pass  United States
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silver mica or polystyrene
Consider that what you are trying to do here is trim
the square wave of an Aleph by have 5 to 20 pF
in the feedback loop. Make the wire too long, say
2 inches, and cut it to trim the square wave.

Turn the amp off when you cut the wire, and dress the
ends slightly apart to avoid arcing.

pass/ - likes the teflon on the wire wrap wire.
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Old 6th February 2003, 09:30 PM   #9
Netlist is offline Netlist  Belgium
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Quote:
Originally posted by Christer


You also need
to know the wire diameter, insulation thickness and the
dielectricity constant for the insulation, but I would guess that
you can get a pretty good accuracy this way.
Christer,
Mr.Pass
If it's that easy I'll remove the 10pF from my BOM!!!

Thanks, I was really afraid I had to calculate that wire-wrap.
I'm so bad in maths


But.... I've got the trick!
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Old 6th February 2003, 09:32 PM   #10
HDTVman is offline HDTVman  United States
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A cap made by twisting 2 wires together that way is called a "gimmick capacitor". Trimming cap values that way has been around forever with RF stuff.

Later
BZ

Christer, you can calulate your self to death but it will be a lot faster to just twist the 2 wires together. The tighter you twist them the higher the C value will go, up to a point.
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