Capacitor polarity question

[Original Burnedfingers]

I have some older Mallory Orange drop capacitors that have a black line on the right side of them. The question is ...is the black line supposed to mean negative or positive? The caps are .22/400V PN PVC4022-10%

Thanks

[Tom Bavis]

No polarity. The "outside foil" is marked with the line - it should go to the lower impedance side of the circuit - usually ground or input. Though it seldom makes any difference...

[Original Burnedfingers]

So it doesn't really make any difference?
Thanks

[Rodeodave]

It can make a difference. Usually something rings less or does not oscillate if connected properly. Also it might help you sleep better...

This might shed some light on the topic: Where to connect outside foil on capacitors


(edit: phrasing and typing)

[tomchr]

The idea is to make the outside layer of foil act as a electrostatic shield for the inside layer. By connecting the outside layer of foil to the lower impedance node, any field lines terminating on the outside foil will cause the least amount of disturbance to the circuit as the lower impedance will require more current to move.

Make sense?

~Tom

[stoc005]

I was taught that the side with the line should go to the grid connection. It helps shield the high impedance of the grid circuit. The other side should go to the plate connection. This is for coupling caps.
If one side goes to ground, the side with the line should go to ground. The active circuit tied to the other end is sort of shielded.
Sometimes it doesn't matter.
Many said the same thing above.

[jjman]

I would think one would want to shield the grid as apposed to using the grid to shield the previous plate. But it hasn't mattered to me and many of the caps I've used don't have the line.

I saw a video on youtube of a guy using a scope to determine which is which. I've tried that with my scope but haven't been able to see a difference. Maybe I don't do it correctly.

[tomchr]

I seem to recall Morgan Jones describing a method for figuring out which pin on the cap connects to the outer layer of foil. I don't recall the methodology, though.

~Tom

[Karsten Sømand]

Originally Posted by tomchr

I seem to recall Morgan Jones describing a method for figuring out which pin on the cap connects to the outer layer of foil. I don't recall the methodology, though.

~Tom

This writing is from Morgan Jones´ book "Building Valve Amplifiers". I can highly recommend to buy this book but also his other book "Valve Amplifiers, 3.rd Edition".

"Unfortunately, the outer foil is not often marked, but it can usually be identified" (see. fig. 3.53 page 163 - not shown in this message!).

"The capacitor under test is connected as a reservoir capacitor to crudely rectified AC, and a strip of metal foil is wrapped around the capacitor. The metal foil is connected to the input of an oscilloscope or an amplifier. If the outer foil of the capacitor is connected to earth, very little noise will be picked up, but if it is connected to the unearthed output of the rectifier, the capacitance between it and the added foil will easily couple the higher harmonics of the rectified AC into the amplifier or oscilloscope. Thus, the outer foil can be identified by finding which connection creates the most noise. Unfortunately, this method doesn´t work for PP capacitors because they are often made from two capacitors in series placed end to end, so they don´t strictly have outer and inner foils".

Hopefully this short explanation helps.

Karsten

PS! DIYAudio Moderator: If the above short writing is against any copyright rules etc. please feel free to remove my writing asap.

[SY]

Probably within Fair Use. No problem.