Outer Foil Test

[glasman]

A couple of months ago I spoke with the sales manager at Sprague on OD's and Rohs. We got to taking about the polarity marks on old series PS caps. His comment was enlightening... "we are using the same equipment today that we used 25 years ago to make these caps and there is no way in hell those old markings meant anything as they never attempted to guarantee polarity".

I ccontinue my diligence today checking every cap I drop on a board..... its laborious, but adds that extra mojo......

Gary

[Funkalicousgroove]

The Dumbles I have seen all seem to have the Marked side of the Cap toward the PT except for the .02 at the entrance of the PI, I wonder..........

[glasman]

The Dumbles I have seen all seem to have the Marked side of the Cap toward the PT except for the .02 at the entrance of the PI, I wonder..........

Not sure what you mean by PT. But they normally point towards the plates. On the PI, the low impedance side is on the input side. The grid side of the PI has an impedance of several megs due to the bootstraping of the PI.

Gary

EDIT: Actually the grid side is probalby in the order of 20 to 40 meg. A DVM will load the heck out of the grid voltage.

[Normster]

The Dumbles I have seen all seem to have the Marked side of the Cap toward the PT except for the .02 at the entrance of the PI, I wonder..........

I think we should start another internet myth that HAD threw away any cap that didn't have the foil connected to the right-hand side when looking at the marked side.

FWIW, I once did a "spec" build that included measuring everything, using only components within close tolerances, orienting caps for polarity, etc. The result was no better than any other build I've done and in some aspects, not as good. On the cap issue, the Dumble design is pretty solid and not prone to pick up extraneous noise so you may or may not notice any difference.

[odourboy]

The Dumbles I have seen all seem to have the Marked side of the Cap toward the PT except for the .02 at the entrance of the PI, I wonder..........

80% of the PS caps in my last batch I tested had the 'foil side' on the lead to the left of the writing. Coincidence? I think not!

[paulster]

80% of the PS caps in my last batch I tested had the 'foil side' on the lead to the left of the writing. Coincidence? I think not!

They probably travel on a conveyor or something similar from production to printing if they do it all in one go, so there is a good chance they'll land the same way round, rather than a certainty that they keep track of the orientation.

[Fischerman]

Scott,
You misunderstood my post. I was testing for outer foil orientation and marking my caps...that's it. I had read long ago that the line didn't mean anything but I had never tested it myself. Now I have. Pretty simple.

[Chicken Head Red]

Where is a good place to get ground clips for probes? My scope is so old and I need some new clips, Mine are hangin on for dear life!!

J.B. Saunders. Boulder. Also good for connectors And miscellany

[gearhead]

I also learned to not disconnect the negative lead of the scope until I marked the cap...too easy to disconnect the leads and then think; "Wait...which side was outer foil again?". But if you're not as fry-brained as me you could get away with it.

Lastly, my scope probe has a clip for the negative but just a point for the positive. Connecting a short wire with alligator clips on each end to the point (to make it easier to clip both + and - leads to the cap) was a deal-breaker. Tons of extra noise. Need to get a 'clip tip' for that probe.

Isn't there another way to test for this? I remember reading about using aluminum (aluminium, lol) foil, the outer casing, certain lead connections, and a good VOM, but just cannot find it again. No OScope yet for me

[heisthl]

If your VOM does capacitance you can put some foil around the cap and with the + lead on the foil move the - lead to find the lead that gives the biggest capacitance reading. Mark that lead as the shield.

[Johnhenry]

Guy's, I love this thread, Great Read, but, take the cover off the orange drop and you look at the way the wire is attached on each end of the roll of foil and then tell me what you think about "POLARITY"
Johnhenry

[gearhead]

If your VOM does capacitance you can put some foil around the cap and with the + lead on the foil move the - lead to find the lead that gives the biggest capacitance reading. Mark that lead as the shield.

Thanks, that's the one!

[Fischerman]

Guy's, I love this thread, Great Read, but, take the cover off the orange drop and you look at the way the wire is attached on each end of the roll of foil and then tell me what you think about "POLARITY"

The .1uF caps I tested had very little noise but some of the smaller value ones had way more. In any case, what you see on the scope will tell you for sure whether it's there and how much.

[Funkalicousgroove]

Where is a good place to get ground clips for probes? My scope is so old and I need some new clips, Mine are hangin on for dear life!!

J.B. Saunders. Boulder. Also good for connectors And miscellany

Been there, they didn't have any, but they did have a good selection of stuff nobody else wants!!

It's actually a really cool store, I spent like 3hrs there!

[glasman]

Try www.circuitspecialists.com

They have a good selection of the right stuff. It is where I buy a lot of test leads and things.

Gary