Capacitor question

[Crash]

OK guys, how does one determine the type of cap to use for a project? There is polyfilm, tantalum, electrolytic, etc. I am recapping a couple of old Altec 436C comps where c2, 3, 5, 6 call for an .022 mfd, ± 10%, 600v cap but I am stumped on the type. Help this idiot out...my head is a spinnin'.

 

[chr1s]

Generally electrolytic caps are for bigger values when the polarity doesn't change, tantalum are quite like electrolytic and foil are for smaller values and when you are not shure about changes in the DC polarity applied to the cap.

22uF (=.022 mfd) would be a electrolyic cap (I suppose it is in the PSU), but I don't know about 600 V caps. The highest values I know from is 550 V, and these are hard to find.


Chris

 

[Crash]

Thanks Chris. Here is a PDF of the schematics along with the part sheet. Everytime I go inside this thing, it looks like everything is tied to everything. These caps are in the audio path it looks like to me but keep in mind I am more of a user with these things than a fixer or tech type.

http://www.dvq.com/hifi/images/436c.pdf

It looks like I was wrong on the 600 volts part. It looks to be 400 volts.

 

[mcs]

[quote author="chr1s"]22uF (=.022 mfd) would be a electrolyic cap[/quote]
NO. .022 MFD is an old abbreviation - MFD means microfarads. So 0.022 MFD is actually 22nF (or 0.022µF). A 22nF 600V cap is normally polyester or polypropylene - the old ones may be paper caps.

Best regards,

Mikkel C. Simonsen

 

[Crash]

Well this is interesting, I have two PDF's of the schematics one showing 400 volts the other 600 volts for the same caps....wonder which is correct? They both look like scans of Altec sheets.

 

[mcs]

Doesn't really matter if they are 400V or 600V types. You can just get the 600V (or 630V) types that are easy to get. Even 1000V or 1500V types are no problem to get.

Best regards,

Mikkel C. Simonsen

 

[Crash]

Cool...thanks guys.

 

[skipwave]

They are .022 MFD, as in MicroFarad or sometimes written uF (where the u is supposed to be the Greek letter μ). Copy this whole URL since the forum software breaks the link at the open paren: http://en.wikipedia.org/wiki/Mu_(letter)

Equal to 22 NanoFarads nF, or 22,000 PicoFarads pF.
http://www.csgnetwork.com/capcodeinfo.html

These are relatively low value caps, which can be used without detriment to bandwidth thanks to the high output impedance of the 6CG7s plate. In general small triodes have high plate impedance, which (in shunt fed arrangements) is in parallel with a high value plate resistor, commonly 100k ohms and up.

In this circuit the 6CG7's plates are driving the 6AL5's cathodes, and those 220k resistors going to the P3 balance potentiometer. So the 6CG7 plate is working into a nice higher impedance, thus the filter formed by the DC blocking caps and the impedances does not require a large capacitor for good low end response. This is unlike low impedance output stages (cathode followers in tubeworld and emitter followers in sandstate), which typically require large value blocking capacitors.

 

[Crash]

I love you guys...this is the place to come when I have a serious no mess around component level question. It is a shame that I don't qualify for the propellerhead beanie cap to understand all that is being said on here. :grin:

Thanks again all.

 

[chr1s]

[quote author="mcs"][quote author="chr1s"]22uF (=.022 mfd) would be a electrolyic cap[/quote]
NO. .022 MFD is an old abbreviation - MFD means microfarads. So 0.022 MFD is actually 22nF (or 0.022µF).
[/quote]
Thanks for the correction, I (obviously) didn't knew that.

Chris

 

[JohnRoberts]

OK for TMI...

mF is short for mmF which is same as uF. (actually mu not u).

In general you use the best cap that will fit or you can afford. Film caps are better than electrolytic but increasing size become prohibitive for larger values.

Answer is often a balance of several factors, size, cost, application.

JR

 

[mcs]

[quote author="JohnRoberts"]mF is short for mmF which is same as uF. (actually mu not u).[/quote]
Not always - on new/recent schematics mF means millifarad. So you have to judge what a reasonable value would be to be sure :wink:

Best regards,

Mikkel C. Simonsen

 

[moamps]

mmF is short for "micro-micro Farad" or "pF".

Regards,
Milan

 

[JohnRoberts]

My bad milli, nanno, micro... mu

I was thinking milli-milli instead of micro-micro.. but wrong is wrong so mea-mea culpa.

JR

 

[bcarso]

And added to the top we have zetta and yotta (10^21, 10^24), at the bottom zetto and yocto (10^-21, 10^-24).

 

[JohnRoberts]

We don't need a new battery for electric cars just give me a yotta Farads.

JR

 

[moamps]

[quote author="JohnRoberts"]...just give me a yotta Farads..[/quote]

..already fully charged, of course. :wink:
An empty one is useless.

Regards,
Milan

 

[JohnRoberts]

like a battery?

JR

 

[moamps]

Yes.
Charging the 1yF cap will last practicaly forever.
(t=C*V/I)

Regards,
Milan

 

[leigh]

Well this is interesting, I have two PDF's of the schematics one showing 400 volts the other 600 volts for the same caps....wonder which is correct? They both look like scans of Altec sheets.

FYI, I have an original Altec sheet, and it says 600 VDC. The PDF you linked to isn't a true scan - the layout and the images are the same, but all the words have been replaced by text data - great for searching within a PDF. However, this little tidbit got lost somehow in translation.

Leigh