Outer Foil Test

[Fischerman]

Another recent thread got me motivated to try this. I decided to check some of my caps for outer foil orientation and the first thing I noticed is that the line on my 6PS caps did not correspond to the outer foil. In fact...most of the ones I checked (only a dozen or so) were 'backwards from the way it was marked. Only two were 'correct' per the marking (these were all the same value caps).

I also noticed that, in general, the smaller the cap value the more 'noise' I saw. In the case of the smallest ones I didn't need to grab it with my fingers...just hooking it up was all that was required. Actually...this was true for all of them but much less so for larger values. Hard to even see it with a .1uF. But in every case, the 'wrong' way was about twice as much noise as the 'correct' way.

And of course...Murphy's Law reared it's ugly head in my D-proto. If I hadn't checked them, they would have all been wrong. But since I did pull them out and check them...every single one I checked already had the outer foil connected to the lower impedance side. There were a few I didn't check but I went through the entire preamp plus the PI input cap and every one was correct. Oh well, I'll sleep better now.

I just marked them using a silver Sharpie and put a little mark right where the lead meets the orange...you would never notice it unless you looked for it (since the silver ink looks so similar to the lead). 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.

Any of this sound wrong or unusual? Any other comments?

[Normster]

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?".

I thought I was the only one who did that.

[JimiB]

sounds all to familiar - wait what was that voltage again?

[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!!

[ayan]

Another recent thread got me motivated to try this. I decided to check some of my caps for outer foil orientation and the first thing I noticed is that the line on my 6PS caps did not correspond to the outer foil. In fact...most of the ones I checked (only a dozen or so) were 'backwards from the way it was marked. Only two were 'correct' per the marking (these were all the same value caps).Any other comments?

The firs thought that pops in my head is that Dumble used old ODs with lines some times, and he always put the lined part of the cap towards the lower impedance side. Provided his caps were incorrectly marked, like some of yours were, could we infer that perhaps he is NOT going for consistent orientation? Ha ha -- I mean it though.

Gil

[dogears]

Are these old old PS series?? The new ones are not marked for polarity. I have never tested the old ones that have the big line. The newer Dumbles I have been in are unmarked for polarity.

Another recent thread got me motivated to try this. I decided to check some of my caps for outer foil orientation and the first thing I noticed is that the line on my 6PS caps did not correspond to the outer foil. In fact...most of the ones I checked (only a dozen or so) were 'backwards from the way it was marked. Only two were 'correct' per the marking (these were all the same value caps).

[Pete]

Didn't see the thread you refer to, could you point me to it? and/or how are you checking the cap, is a scope all that is needed? I'd like to learn how to do it. Thank you

Another recent thread got me motivated to try this. I decided to check some of my caps for outer foil orientation and the first thing I noticed is that the line on my 6PS caps did not correspond to the outer foil.

[Fischerman]

Scott,
These are from a very recent order from Mouser (I think it was Mouser). All of the ones I got had the fat line at one end. But I only bought a few 6PS...most of mine are 225P and have no line.

Gil,
I hear ya...maybe a few were intentionally and 'strategically' placed with the outer foil to the high impedance side to induce a little more coupling. It also seems that there are a few places where it doesn't matter much...or maybe turning a knob switches the low impedance side. Seems like the HRM bass cap is like that. It seems with with bass at low settings the low impedance side is the ground side but with the pot at high settings the lower impedance side is the slope resistor side. Or the Skyliner mid-cap...250k pot to ground and 150k slope+100k plate on the other...so that one's a push right (with pot on 10)?

Pete,
I think it was glasman's combo thread in the Files section. There is also a short paper on it on Aiken's site.

[dogears]

Matt,

Your test is meaningless. The new PS caps are not polarized. Question is whether the old ones, with the super fat line (not like now) are. All bets off until we measure some NOS caps.

[odourboy]

Matt,

Your test is meaningless.

If his test was meaningless, then why is one orientation (presumably outer foil wrap side to ground) less noise sensitive than the other?

[heisthl]

Didn't see the thread you refer to, could you point me to it? and/or how are you checking the cap, is a scope all that is needed? I'd like to learn how to do it. Thank you

Another recent thread got me motivated to try this. I decided to check some of my caps for outer foil orientation and the first thing I noticed is that the line on my 6PS caps did not correspond to the outer foil.

Probe on one leg scope ground on the other. Grab the cap and watch the noise on the scope. Switch the leads, grab the cap and watch the noise. The most noise means your probe is on the outside foil terminal. Mark the leg, pretend its a shield.

[mdroberts1243]

Any of this sound wrong or unusual? Any other comments?

Couple additional comments...

Some of the larger values are probably built with multiple sections that will cancel a polarity effect.

When I tested and marked all my 6PS for a recent build I found that the labels were random, so you couldn't count on them to be consistent, even within a particular value, for 'polarity'. The SBE 6PS that I use don't have a black band.

[heisthl]

I wonder if anyone has ever actually seen a difference with the "correct" orientation. Sure the high impedance side is more prone to noise sensitivity so should be "sheilded" with the low impedance side right? Well what about the opposite - I have this big plate signal and I'm going to attach it to this big outside foil antenna? That may work out to be more noisy in the long run when neighboring components are taken into account.

[dogears]

You misunderstood my post. Matt was testing the orientation of the foil of his "new" PS caps as relates to the lines on them. It is common knowledge that SBE corp randomly marks the caps. So testing them versus the line orientation is moot.

Of course, the test is good as are the results!! Foil to low impedence.

Matt,

Your test is meaningless.

If his test was meaningless, then why is one orientation (presumably outer foil wrap side to ground) less noise sensitive than the other?

[odourboy]

Yep... I misunderstood your post.

You misunderstood my post. Matt was testing the orientation of the foil of his "new" PS caps as relates to the lines on them. It is common knowledge that SBE corp randomly marks the caps. So testing them versus the line orientation is moot.

Of course, the test is good as are the results!! Foil to low impedence.

Matt,

Your test is meaningless.

If his test was meaningless, then why is one orientation (presumably outer foil wrap side to ground) less noise sensitive than the other?