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Old 8th November 2006, 01:57 PM   #1
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Default Teflon capacitor bargain!

I just found a pair of 0.47uF 200V russian military teflon capacitors on ebay (SOVCOM ebay shop) and bought them immediately.

The pair cost $40 including shipping to the UK!

Probably worth checking out the other stuff at this ebay store....

Question: sorry to be dumb but what would the corner frequency be if I used these as input coupling caps on a Peter Daniels gainclone, if placed before a 100K pot? I know the formula, but don't know how to work out the input impedance of the amp including the pot...

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Old 17th November 2006, 03:32 AM   #2
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Just found another pair of the same but I don't need them, so someone might want them:

Ebay Russian Teflon 0.47uF capacitors (x2)
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Old 17th November 2006, 06:02 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
the 100k pot is followed by what Zin?
If it were another 100K then the cap would see a variation between 100k and 50k as the effective Zin.
The -3db frequency would be
1/2piRC=1/2*Pi*50k*0.47*10^-6=6.8Hz when volume is set to maximum.
Or 3.4Hz when attenuated to maximum.
BUT the effect of the high pass filter will extend up to about a full decade above the turnover frequency. i.e. 68Hz.
That is effectively a variable bass cut filter each time you adjust the volume control.

As amplifier Zin drops the bass cut gets worse.

AND if the source also has a DC blocking capacitor, then you have to calculate that effect (worse still) as well.

470nF works well for tube types since their impedances are generally higher.

Solid state tends to favour 2.2uF upto 10uF as DC blocking between source and receiver

PS.
what does 200B mean? Vac? Vdc? Vpeak? DC working V?
and
MK(phi) metallised film?
I have paper in oil and they are MK(phi) and 300B to 400B
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Old 17th November 2006, 07:47 PM   #4
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Quote:
200B
It's not 200B, but 200V. Vdc.

What looks like the capital letter B is v in the Russian alfabet, ve in phonetic writing.
Only a, e and k(sort of), m, o, t, and x are the same.

The MK(phi) is Russian for MKF, which stands for uF, 0.47uF !
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