Help determining outer foil, I have tried every method documented.

[Bangy]

For a week I have been trying to find a method that shows definitive, repeatable, results when testing Caps for the outer foil. I have tried the foil around the cap, with the Oscilloscope probe on the foil, Using my fingers as an antenna, using an amp with an input jack with a cap- and I see no discernabale consistent results.  Both ways of hooking up the cap seem the same, no magintude difference.  The interference looks the same.

Ive tried Sozo's which have an outer foil delineation line- No dif
I have read the threads on the forum.

Ive tried older blue molded caps from Fender amps - No dif
Ive tried NOS mustard caps (which is what Im really hoping to figure out) and no dif.
I even built the little circuit that Eric Barbour recommended in issue 17 of Vacumm Tube Valley- and again no definitive results.


A very good source has told me Mustards need to be checked individually, in other words there is no method to the outer foil, such as the beginning of the writing or. . . ????

If someone has a method that works for them, would you mind explaining how in the world you were able to discern the differences???

Cheers

[BetterOffShred]

http://el34world.com/Forum/index.php?topic=19534.0
Which you said you read already ..

This subject is contained in that link, and there's a few different types of things happening.   I've tried it myself, and I don't think I really hear much of a difference with most caps either.   That being said, I believe in the capacitor Placebo effect.. where if you know you have a 5 cent pile of manure Ceramic capacitor stowed away inside your precious amp, your brain might betray you and tell you that it should sound better with a $5 cap in there.  And it may..  But I've been unable to hear much of a difference with how I usually play my amps.  I do like to use quality components just for posterity, so that's what I do.  It's just got a ton of subjectivity to it.  There was a thread over on TDPRI about it where a guy ran a bunch of tests with a scope and everything, but nobody ever came up with good straight answer on it.
I myself used the guitar cable technique into a tube amp turned up a ways, didn't hear much if any differences!  Just saying
-Brett

[Bangy]

Thanks Brett. Yea the testing techniques seem to be  great on paper, but in practice I have not found a definitive method.  I have been concentrating on the scope ideas, maybe I will revisit the amp idea and see if I hear any remote difference. As far as the rationale for implementing the foil-side shenanghins, I am trying to recreate a 5F6A. I have an original OT, selenium rectifier, AB CC resistors, even a NOS grey cord and Im using NOS mustards that all test great, no leakage and spot on capacitance. Im geeking out on this one i know -- because I love the sound of my 'Lili' built 5F6A, trying to leave as little possible to chance.

The next one (I am into building pairs)  will be more of a Hybird go with 'improvements t functionality.

I welcome ideas if anyone had luck determining the outer foil and would be willing to share the finer details of just how they pulled things off.

BAngy

[Tone Junkie]

I made the foil tester. I found it works better on a loud amp. some caps I can here a huge difference others nothing at all. I built tester you can flip the direction quickly with a switch, that helped greatly . I have problems with my mustard caps also.
Bill

[Willabe]

I made the tester box with switches and alligator clips.

I found that the smaller the value of uF the harder it was for me to hear any difference. The little .005 (.0047 modern value) that's used in a Fender 1 knob tone control was almost impossible to hear any difference.

For Tubnite and Geezer it was the opposite, the larger the uF value the harder it was for them to hear any difference. I have no idea why that is. 

There were a few guys here that posted they couldn't hear a difference and when asked what amp they were using to test with it was a solid state amp. They then tried a tube amp and said they could then hear a difference. 

I was testing different caps of the same value on my bread board (BB) to see if I could hear any difference in tone, all of the same uF value, .02, I could hear a deference. It was small but it was there. I tested ~20 caps? So before I soldered them to a 12 position rotary switch on my BB I tested them for their outside foil lead. A few, 2 or 3(?) were much less noticeable, but, I could hear the difference, all the others were pretty easy to hear. The hard 1's to hear were hi end audio caps.   

[Willabe]

And you read this thread too?

http://el34world.com/Forum/index.php?topic=11427.0

[MFowler]

https://www.youtube.com/watch?v=BnR_DLd1PDI

[drgonzonm]

http://www.youtube.com/watch?v=BnR_DLd1PDI

Yes

[Katie 77]

Rube Goldberg Method
https://www.youtube.com/watch?v=Qu_FrHdUUNs

[EKDENTON]

You don't need to build an elaborate test device. Just clip the leads on the capacitor, set your scope on the lowest voltage and divisions. Then pinch the capacitor between your fingers. reverse the leads, pinch the capacitor and check again. The position with the least amount of noise will be when the scope ground lead is on the side with the outer foil.


You can also just hold the capacitor close to the scope monitor tube and it will pick up noise then reverse the leads and hold it to the scope monitor tube again. I have found that there is not much difference with larger capacitors but the very small caps like the ones you use in the first gain stages seem to have about 1-1/2 times the noise signal when the leads are reversed. With .1 or larger i can not see much difference.

[Ed_Chambley]

And when you do find it, you are "supposed" to position the outer foil towards the lower impedance of the signal.  In short, I have been told "towards the previous stage."  Is the previous stage always lower impedance?  When is it and when is it not?  Not being funny, I really don't know the answer.


I have been trying for a week now to understand Cathode Followers and yes I have read the Valve Wizard and many other write-ups.  I know the CF lowers the impedance, in most cases to around 615 ohms.  So does the cap following the CF's outer foil position towards the Signal or Towards the Tone Stack in a CF driven tone stack.


What I am getting at is even if you find the outer foil, you still have to know how to install it.  I have not read a lot of discussion on this.

[shooter]

position the outer foil towards the lower impedance of the signal.

I understood?this to mean "least" resistance to ground, so in a typical CF the cathode R might be 100k, then cap to say a TS with a 39k slope, 1M pot.  the "least" R's to ground would still be the 100k, I'm probably missing some magic lightbulb yet to light though

[Ed_Chambley]

position the outer foil towards the lower impedance of the signal.

I understood?this to mean "least" resistance to ground, so in a typical CF the cathode R might be 100k, then cap to say a TS with a 39k slope, 1M pot.  the "least" R's to ground would still be the 100k, I'm probably missing some magic lightbulb yet to light though

Yes, the same light bulb that went off when I was told something.  If what you are saying is true, how could a signal ever pass through the tone stack?  This is where I get lost often.  Impedance!


I keep on asking this stuff and one day I will understand it.  It is much easier to steal and tweak than it is to figure out how it works!

[PRR]

> in a typical CF the cathode R might be 100k, then cap to say a TS with a 39k slope

The signal impedance is the ~~1K of the *cathode*, parallel with the 100K DC path resistor.

[EKDENTON]

What I am getting at is even if you find the outer foil, you still have to know how to install it.  I have not read a lot of discussion on this.

From what I understand on what i read about it (most of that i take with a grain of salt) that when their is a plate preceding the cap then the foil side goes towards the plate of the previous tube. If their is not a preceding tube then the shield side should be on the side nearest a ground.  I think i said that right.....LOL it has been several months since i studied it. anyway i marked in the photo where i believe they go. except for the cathode off the PI I was not sure which direction would be best, however at this point in the signal path their may not be much difference which way it is turned. I think the important ones are at the beginning of the gain stages.

[drew]

Where the stripes go on a Dumble-type amp: http://ampgarage.com/forum/viewtopic.php?f=4&t=24654&p=374387#p374387

[EKDENTON]

The type amp does not matter, just use the same principal for any amp. 


Follow the signal path on the schematic, and....then



positioning the shielded side away from a gain stage grid would probably be the best idea. 

[jojokeo]

From what I understand on what i read about it (most of that i take with a grain of salt) that when their is a plate preceding the cap then the foil side goes towards the plate of the previous tube. If their is not a preceding tube then the shield side should be on the side nearest a ground.  I think i said that right.....LOL

No, that is exactly correct Ed! No more complicated than that!


As for testing without a scope I find it best to use a fuzz or distortion pedal to help hear the background noise. You must always hold/pinch the cap under test no matter which method you use. This is mandatory. Lastly another hot tip is to make a set-up which you can alligator clip to your caps for quick testing of multiple caps and wire in a toggle switch. This is very helpful when listening for the subtle difference between the two positions.


Remember that there are certain caps that don't have an outside foil due to how they are made/compsition and as the cap's size gets larger - up to .1uF and bigger - the more difficult they are to discern.

[Ed_Chambley]

Yep, I have had it explained as simply consider the outer foil the negative. Sort of like a Diode.  I posed the question for 2 reasons. First, I began hearing this year's back, but Randall Akin had written a write up I read long before I saw any youtube stuff and if I recall he mentions  the od715 does not apply.


Secondly, people mention this, but I rarely hear how to apply, so I thought I would mention it in case someone may be too shy to ask.


I do not mind saying what I do not understand. So let me ask this. In a say fender blackface tone stack, the 3 blocking caps that create the eq. No matter where you adjust the pots the signal will always pass through the cap in the same direction? If so, all the outer foil should be towards the plate? I understand this section to be responsible for the tone and is ac impedance. So even if treble mIddle and bass are zero, it is still greater impedance than the driving stage?


I do not understand how tone sacks really function. I use Duncan and understand frequency, high pass and low pass and some of divider networks, but the resistors being adjustable messes with my mind a little to be honest.


Also, those old amps a lot of us love for their character were not built using this idea. I know as I checked my originals only to find I know tweeds, Brown, black, silver face and my plexi and 66 jtm 45 all have random outer foil position. Aston caps are marked, but if you check them you will find the line not correct all the time.


I have even ran across sozo caps like this, but only 2.


Is it possible this haphazard approach created those amps with something special. You know what I mean, 2 amps built the same.but one just plays and feels better. I have had 2 Marshall amps, both the same year and model, one just was much better even if you swapped tubes.


And you build pedals. Do you think it applies here? If not, do you think it is due to low voltage? On a transistor, should the outer foil be towards the emitter?


I will say using a scope is easy, but you can also wrap foil around the cap and apply ac, no voltage outer, some voltage inner. This is the general way hifI builders check. Even with the hifi builders who are much more invested in caps, by the majority do not concern themselves with modern cap orientation, but most use supercaps too.


I still mark caps, my amps are quiet. I actually built an se amp with all installed backwards. Checked noise and then flipped them. No difference, but I did use NOS aerovox caps. Could be the reason.


Not being argumentative, but I have read a lot of seasoned builders say the low impedance side is not always as obvious as one may think. I even hear the outer foil should be towards the lower voltage.


This being written, I really would like someone to explain some of what is going on in the T M B stack. With the Duncan software I can check and see, but I really don't get it all that well. Difficult to see exactly on my scope, but that is probably because I am not sure how to connect because I don't know how it works. If I keep reading, I am sure I will, l get it soon. Help is always welcome.

[jojokeo]

I've attempted to answer about four times so far but btwn work and iPhone I hope to finally get it done? Not that it will likely answer all your questions?
My feeling and opinion is it does matter but just how much? This is the question? If you can hear the hiss louder in one direction as to the other by using sound through amp method then there has to be something to it. But I think it's a tough nut to crack definitely? I don't let it make or break the belief that an amp simply must have done this to be considered top notch. But, if I go through my cap bins and they've been tested and marked I will pick those and install them appropriately for sure. I've also tested specifically to mount them properly on builds too. I will usually do things to the best ways that I know either way. Call it being anal or conciencious or attention to detail, etc.


Orange drops can be tested but caps like silver mica, teflon, and ceramic types cannot since they aren't layered.


Tonestacks - the signal passes through them for all intents and purposes in one direction - at least initially and that's what matters. Put the foil sides towards the prior plate. On a Presence pot it would go towards ground. But I don't think this one has much if any affect. To me it's coupling caps that matter most. Then the tone stack stack caps. And if using a non-polar cap on a cathode bypass then the foil goes towards ground. If you were to use a cap across a plate load resistor then the foil would go towards the filter cap side feeding the plate. This pretty much covers it all?


On my pedals I've tried it but don't think it really matters. As you've said being low DC voltage inside most of them - impedance is different and is thought of the same as resistance mostly. In AC powered circuits you have reactance which is capacitance and inductance.

[Ed_Chambley]

I've attempted to answer about four times so far but btwn work and iPhone I hope to finally get it done? Not that it will likely answer all your questions?
My feeling and opinion is it does matter but just how much? This is the question? If you can hear the hiss louder in one direction as to the other by using sound through amp method then there has to be something to it. But I think it's a tough nut to crack definitely? I don't let it make or break the belief that an amp simply must have done this to be considered top notch. But, if I go through my cap bins and they've been tested and marked I will pick those and install them appropriately for sure. I've also tested specifically to mount them properly on builds too. I will usually do things to the best ways that I know either way. Call it being anal or conciencious or attention to detail, etc.


Orange drops can be tested but caps like silver mica, teflon, and ceramic types cannot since they aren't layered.


Tonestacks - the signal passes through them for all intents and purposes in one direction - at least initially and that's what matters. Put the foil sides towards the prior plate. On a Presence pot it would go towards ground. But I don't think this one has much if any affect. To me it's coupling caps that matter most. Then the tone stack stack caps. And if using a non-polar cap on a cathode bypass then the foil goes towards ground. If you were to use a cap across a plate load resistor then the foil would go towards the filter cap side feeding the plate. This pretty much covers it all?


On my pedals I've tried it but don't think it really matters. As you've said being low DC voltage inside most of them - impedance is different and is thought of the same as resistance mostly. In AC powered circuits you have reactance which is capacitance and inductance.

I am with you Joe.  I mark them and install them as has been described.  I cannot remember, but the article I read by Randall Aiken here:
http://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors


States the Orange Drop 716P is spiral and thus does not have a particular "outer foil".


It is very easy to do, so I just mark them prior to putting them in their storage bins.  I actually have switched to using Solen caps.  Why?  Same reason I used to use Sozo, I got a load of them for next to nothing.  Still like to play around with them.  These along with the Red Audiophiler when I do not need a lot of filtration is what I am using right now.  This along with Polystyrene cause again I got a lot cheap and why not, these will last a long time and in a lot of cases I can get away with none or 1 Electrolytic.


I don't think it would be anal.  I have certain ways I do things and that is all this is.  A method is all.  I have heard others mention a lower floor noise and I don't think they are fibbing.


I will say I have found the first coupling cap is important to me and this position I usually will gator clip the cap and change it.  Sort of auditing it.  But then again, I focus first on getting a nice clean tone.  After I get this, then I will begin tweaking for harmonics.  But I don't like amps that dirty up when you don't push them.  I can get it to scream, plus I am not a huge fan of a 12Ax7 clipping too hard, but you know this.  We have discussed this before.


But having a method of builds is important even if someone does say it doesn't help, I disagree.  These methods form consistency and this is reason enough. least it is to me.

[jojokeo]

I was thinking polystyrene but had a brain fart however I think I've seen them listed as teflon on eBay? They are expensive for the right voltage ratings and tight tolerances. I heard they can sound sterile like using 1% metal film resistors. 😏 (Psyche! Just messing with some people that may read this?)


Orange drop being spiral? Makes me think of a orange sherbet ice cream 🍦 damn its hot outside right now and sounds good. Consistency is important and I can think of a lot of reasons and examples. I used to read Aiken along with Blencowe, Weber, Jones, etc almost daily but it's been a while. Last time I think was when I designed a pi using an au7 tube last year?


I think it was tubenit that also thought the first coupling cap was pretty important in making a big difference?


I'm down to final assembly on a new design that's going to use all Mallories this go 'round. I'm even using a couple of old yellows in there. Speaking of Duncan stack generator I found and am using a new set of values that I'm really looking forward to hearing and using on this one. I spent about 3 or 4 hours modeling until this was realized. I started seeing relationships and things and using the screenshot traces really helped.


I normally go 250k on treb and 1M on bass but this does the opposite. Then believe it or not the slope resistor goes up to 220k! The notch is exactly where I want it and the amount of dip too. Plus with the right mid value it looks to be very good. The caps changed just a tad as well. I'm using an EF86 on this one and it doesn't have quite the usual loss. Anyway...I'll know soon. 😎

[Ed_Chambley]

I was thinking polystyrene but had a brain fart however I think I've seen them listed as teflon on eBay? They are expensive for the right voltage ratings and tight tolerances. I heard they can sound sterile like using 1% metal film resistors. 😏 (Psyche! Just messing with some people that may read this?)


Orange drop being spiral? Makes me think of a orange sherbet ice cream 🍦 damn its hot outside right now and sounds good. Consistency is important and I can think of a lot of reasons and examples. I used to read Aiken along with Blencowe, Weber, Jones, etc almost daily but it's been a while. Last time I think was when I designed a pi using an au7 tube last year?


I think it was tubenit that also thought the first coupling cap was pretty important in making a big difference?


I'm down to final assembly on a new design that's going to use all Mallories this go 'round. I'm even using a couple of old yellows in there. Speaking of Duncan stack generator I found and am using a new set of values that I'm really looking forward to hearing and using on this one. I spent about 3 or 4 hours modeling until this was realized. I started seeing relationships and things and using the screenshot traces really helped.


I normally go 250k on treb and 1M on bass but this does the opposite. Then believe it or not the slope resistor goes up to 220k! The notch is exactly where I want it and the amount of dip too. Plus with the right mid value it looks to be very good. The caps changed just a tad as well. I'm using an EF86 on this one and it doesn't have quite the usual loss. Anyway...I'll know soon. 😎

Sounds interesting as I have never considered upping the slope over Fender 100K and normally prefer lower.  I have begun using a Pot for a slope is some instances.  This adds a lot of options.


1 Meg Treble and 250 K Bass?  Are you using a mid?  Seems reversing them in this way would put a lot of mids available in the treble control.  Anyway, this is why I like the hobby.  Break some rules and see what happens.  Most times I end up taking it apart because it dod not work out and that is why I am building this breadboard.


This reminds me, I have done a lot more to it I need to get photos of and post.

[jojokeo]

Sounds interesting as I have never considered upping the slope over Fender 100K and normally prefer lower.  I have begun using a Pot for a slope is some instances.  This adds a lot of options.


1 Meg Treble and 250 K Bass?  Are you using a mid?  Seems reversing them in this way would put a lot of mids available in the treble control.  Anyway, this is why I like the hobby.  Break some rules and see what happens.  Most times I end up taking it apart because it dod not work out and that is why I am building this breadboard.


This reminds me, I have done a lot more to it I need to get photos of and post.

Yes post pics - big bread boards with amp circuits look like Frankenstein's laboratory! You just need to put a few beakers with dry ice bubbling and smoking nearby for the photoshoot!

Yes, I'm using a Midrange pot and it's very important to the overall stack operation giving it much versatility too. I got some cool NOS 16K types with a pushpull switch that I've been wanting to use for a while and put one to use on this build. It's a little different from most switched pots in that it's normally open pull to close. So they can't be used for "lifting" duties as I hoped when I got them. I'm using it for NFB control where pushed in there's no feedback and pulled it's engages it.

[Techineer]

I see at least an implied question in this thread regarding how the outside foil connection affects "tone".  Short answer - It doesn't.

The reason the outside foil connection is an issue is because that outside foil is more susceptible to pickup of noise than the inner foil, as the outside foil tends to shield the inside foil.  The outside foil then becomes a possible source of noise picked up from stray electrostatic and electromagnetic fields. 

If the amp is otherwise well shielded and has no internal radiated fields, you would not be able to hear any difference regardless of which way the capacitor was connected.

If the lead connected to the outside foil is grounded, then any noise picked up by the outside foil is immediately conducted to ground, and has minimal effect on the circuit.  As a coupling capacitor, connecting the outside foil lead to the plate of the tube (a low-impedance point) permits the tube to overwhelm the noise, as noise tends to be a high-impedance signal.

The method described about using a scope probe is the simplest one and seems to work well.... for more details see  http://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors

[pdf64]

...If the amp is otherwise well shielded and has no internal radiated fields, you would not be able to hear any difference regardless of which way the capacitor was connected...

My understanding is that an amp will be chocka full of internal fields; parasitic coupling will tend to link everything to everything else, to some degree. A benefit of the 'outer foil connected to the lowest impedance' thing is that it may help to reduce that.

[ALBATROS1234]

check this video out

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