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Old 30th May 2020, 1:23 am   #1
joebog1
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Default NOS capacitors

So the capacitors that I ordered a couple of months ago have arrived. PIO military types.
They were made around 1964 ( a few different dates). So I have measured them and they would seem perfect for my audiophoolery . Circuit requirements call for .5Uf coupling capacitors, so I will parallel two of these up to give me something very close to that value.
There are only two capacitors in the audio path, those being the couplers from the phase splitter to the driver valves fot the push/pull output quad.

I did notice that they have quite high inductance, and with a bit of thought I will parallel them in opposite directions to try and counter that somewhat. Initial tests show I can reduce that inductance to almost zero. So I have a couple of questions!. Does my audiophoolery thoughts on reducing that inductance make sense, or am I just being silly?.

Note the glass end seals on these caps !!

Some pictures to show what quality meant back in the 1960's

Joe
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Old 30th May 2020, 10:57 am   #2
duncanlowe
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Default Re: NOS capacitors

22 MegaFarads. Wow!
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Old 30th May 2020, 11:02 am   #3
M0FYA Andy
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Default Re: NOS capacitors

I think MFD is a fairly standard abbreviation for microfarads?

Andy
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Old 30th May 2020, 11:07 am   #4
Amraduk
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Default Re: NOS capacitors

Hello Duncan,

Quote:
Originally Posted by duncanlowe View Post
22 MegaFarads. Wow!
They are 0.22uF, not 22uF!

Regards,

Dave.
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Old 30th May 2020, 11:15 am   #5
duncanlowe
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Default Re: NOS capacitors

Have to admit I missed the decimal point. And I realised it couldn't really be M for Mega, but u is what I'd expect for micro (properly greek mu), and m for milli. Always made me laugh when Tandy advertised radios with 250MW output power using a PP3.
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Old 30th May 2020, 11:16 am   #6
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Default Re: NOS capacitors

Maybe the lack of inductance one way is from you effectively putting together like a non-inductive wirewound resistor?
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Old 30th May 2020, 11:53 am   #7
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Default Re: NOS capacitors

Quote:
Originally Posted by joebog1 View Post
... I did notice that they have quite high inductance, and with a bit of thought I will parallel them in opposite directions to try and counter that somewhat. Initial tests show I can reduce that inductance to almost zero ...
I'm a bit surprised at that. Inductance arises from the energy stored in a magnetic field. To reduce it we need to arrange that opposing fields from different sources (the two different capacitors) overlap in space and so cancel one another. Where, in space, do you think the field for a single capacitor might be strongest, and is it practical to arrange overlap between those regions for two capacitors ?

Cheers,

GJ
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Old 30th May 2020, 2:36 pm   #8
DMcMahon
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Default Re: NOS capacitors

Do not know what type of dielectric medium these capacitors are. If a paper type dielectric than due to age they potentially could have become leaky.

If they are going to see DC voltage like a valve anode to grid coupling capacitor then to be on the safe side, would be worthwhile checking them out for leakage (if you have not already done this of course).
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Old 30th May 2020, 2:56 pm   #9
dazzlevision
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Default Re: NOS capacitors

Quote:
Originally Posted by joebog1 View Post

So, the capacitors that I ordered a couple of months ago have arrived. PIO military types.

Joe

PIO = Paper (dielectric) In Oil
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Old 30th May 2020, 4:49 pm   #10
DMcMahon
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Default Re: NOS capacitors

Aha, I wondered what PIO was
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Old 30th May 2020, 7:40 pm   #11
factory
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Default Re: NOS capacitors

They look like a hermetically sealed metal cased capacitor with plastic cover.
More info here: https://www.parttarget.com/5910-00-8...E-41DE5303C690

They sound better than the plastic PIO Sprague HV capacitors I keep finding in HP oscilloscopes, they definitely leak (their contents everywhere).

David
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Old 30th May 2020, 8:42 pm   #12
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Quote:
or am I just being silly?.
Yes!
 
Old 30th May 2020, 11:45 pm   #13
Herald1360
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Default Re: NOS capacitors

Quote:
Originally Posted by joebog1 View Post

I did notice that they have quite high inductance, and with a bit of thought I will parallel them in opposite directions to try and counter that somewhat. Initial tests show I can reduce that inductance to almost zero. So I have a couple of questions!. Does my audiophoolery thoughts on reducing that inductance make sense, or am I just being silly?.


Joe
Not entirely. Two inductors in parallel without any mutual coupling will behave like resistors in parallel so if they're identical the circuit inductance will be around half that of one on its own.
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