Why is it?

To confuse the hell out of us all?

I dunno -- but if you change the nomenclature on your circuit board to make it more clear, expect to get it back from the assembly house with a bunch of reversed caps.

So it's a consistent standard in a reverse kind of way.

Michael

My guess is that just a - on the circuit board might get interpreted as a "pin 1" mark, mechanical alignment mark, or just a mistake, whereas a

• is less ambiguous. On PC motherboards, I often see a circle around both capacitor leads, with the half-circle around the negative lead filled in.

Sometimes you see the - or the + mark enclosed in a circle, especially around batteries. This might be another attempt to make - less ambiguous.

The next question is why the caps don't have a + mark instead. I have heard that back in tube days, on wound capacitors that weren't even polarized, it was common to mark the lead that went to the outer foil layer. This might have been so you could use it for shielding; it may or may not have gone to a more negative voltage than the other lead. Maybe this is where the idea of "mark the negative" came from.

Matt Roberds

Yup. Outside-foil-to-ground made a big difference.

This might have been so you could use it for shielding; it may

I haven't seen many positive-ground tube circuits.

Could well be. Early metal-can electros were pretty much all intended for positive supplies, being wired with the can as the common negative terminal, but that might explain the marking of axials.

And I've recently come across radial lead electros with the _positive_ side marked with a bar. As the old saying go, "once you've seen one tiger, the woods are full of them."

Cheers

Phil Hobbs

Tantalums generally mark the + side.

These were wet aluminums, though.

Cheers

Phil Hobbs

The line (and it isn't just on electrolytic capacitors, it appears on nonpolarized caps too) indicates the OUTER CASE of the gizmo. For signal-pickup reasons, it sometimes matters. If that outer case can be grounded, signal pickup due to proximity to the component is small.