Jag's Tech Tips - Identifying Capacitor Outside Foil

In this video, I take a break from the Triwatt Build and show you two ways to find which is the outside foil on a foil capacitor.
The Ego continues to blather on about the Finland conspiracy and is still wondering about how marshmallows were invented. He also seems to be leaning toward the “Flat Earth” theory.
The next Triwatt build video should be out in the next week or two, It will be completed and ready for testing!
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[@on1ytheb3st]

Wow what a great explanation; from the break down of signal path and current pathing on the schematics to the examples, this solved a lot of my burning questions! I do have one anomaly on my amp schematic where the phase inverter to power tube coupling caps actually have a resistor between it and the plate of the phase inverter that has a higher value than the resistor between it and the grid of the power tube. In this case should the outer foil be closer to the grid of the power tube or still not?

[@JagStar]

I’d still orient it toward the previous stage. But, that far into the circuit it won’t make much difference either way. Thanks for watching and commenting.

[@on1ytheb3st]

@@JagStar Thanks for the insight. Yeah I was going to go with the method you recommend for most any of the film caps I needed to replace but for more questionable ones I planned to orientate them how the factory had them. Beyond just film cap manufacturers not marking them to begin with, was Fender back in the late 80s early 90s checking for outside foil and considering its orientation during their amp assemblies or likely not?

[@JagStar]

@@on1ytheb3st On most of the amps I’ve seen from the early ‘70’s and before, the caps usually have a band that is “supposed” to mark the outside foil. I’ve tested many and usually the band is correct, but it’s not uncommon for it to be backwards. I think the person working the line would get it wrong on Monday mornings or Friday afternoons. Hang over or anticipation 😂. I think the engineers of the day might have intended the line workers to pay attention to the orientation, but I don’t see a lot of evidence of that on the actual amps. Foil caps are not polarized so they will work either way. Just potentially noisier if the foil isn’t to the “most grounded side” or the circuit.

[@countryside8122]

OK would you do the same thing on a mylar cap or any caps that can be replaced in these old amps and radios? Also can you check them in the circuit or does one end have to be removed to do this test? This is great way to test these. Thank you for the demo.

[@JagStar]

You can do this with any film capacitor that is wound. Generally those are only foil caps. Mylar caps are generally stacked so there isn’t really an outside/inside foil. I’ve never checked them in circuit, but it should still work. Thanks for watching.

[@luminousfractal420]

​@@JagStar watched about three vids before yours. they all reference all caps this way. not spiral wrapped specifically. thanks for pointing that out 👍

[@JagStar]

Thanks for watching. Yes, this only applies to foil caps. Cheers

[@rodolfoamaralguitar]

Hello. Does it affect the the tone of a shielded guitar?

[@JagStar]

No. This is shielding for the components in the amplifier and has no effect directly on the guitar. Thanks for watching.

[@rodolfoamaralguitar]

@@JagStar thanks

[@carlrudd1858]

no

[@michel333100]

Hi Jag, I gave a question for you. I have a Fender Bandmaster Blackface 1965 amp. I notice that all of the Blue molded are all sitting on the circuit board with the foil end with the black circle around the capacitor facing the preamp valves. I thought that the grounded side of the board was the side where the speaker jacks and the on and off switches are. J would think that all of the blue xaps should have the black circle end facing the speaker jacks. Please clarify this for me. Thanks from Michael Newell from Niagara Falls, Ontario

[@JagStar]

From your description, it does sound like the outside foil is not to ground. The black line is supposed to indicate the outside foil but isn’t always right. I’ve tested many that were jacketed the wrong way around. Since the foil caps aren’t polarized, it makes no difference to the functioning of circuit which way around they are installed. Having the outside foil to the ground side can help shield some stray noise but it won’t hurt the amp if it’s the other way around. If your amp is working and sounds good to you the way it is, I wouldn’t worry about it too much. If you ever find yourself replacing the caps or you have a couple hours and want to turn them around, that won’t hurt the amp, but it isn’t strictly necessary. Remember that caps that are polarized, such as electrolytic capacitors, do need to be installed the correct way around for the circuit to operate properly. I’ve never seen a polarized cap that had the markings backwards. I’m sure it happens, but probably not very often and it would be caught during manufacturing and testing of the amp. Thanks for watching.

[@michaelnewell3823]

@@JagStar yeah I have a Ceriatone HRM amp that I just changed a couple of orange drops in. Just wanted to make sure. You are from Edmonton I take it? Heard your band. Really good.

[@redelk2974]

thank you, very informative, interesting

[@JagStar]

Thanks.

[@carlrudd1858]

No need for concern about outside foil with modern film caps etc. Maybe in some outlying instance, depending.

[@philhodson1675]

Which oscilloscope were you using on your laptop??

[@JagStar]

Sorry to be slow responding! I used the software that came with my Sain Smart DS802 USB Oscilloscope. I don't know if it's still available but here's a link,www.amazon.ca/gp/product/B07JR61MM9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1. Thanks for asking!

[@philhodson1675]

Thanks Jag! Will go check it out. Wow oh wow your series has helped me know end. I’m 75% complete ok finishing my custom plexi. Getting excited and nervous about plugging it in for that first time and hoping it works!!!!!

[@JagStar]

@@philhodson1675 Awesome. Thanks for the compliment. Let me know how it goes!

[@nacholibre9929]

Thanks a lot

[@JagStar]

You are very welcome 😊

[@claesmansson9070]

From the beginning it was marked on the caps.

[@JagStar]

Yes, I covered that. The marking is not always correct.

[@jackmatthews2840]

So there is 2 of you?

[@JagStar]

It feels like there should be. 😂 Thanks for watching.

[@martinlicht1969]

How hard who it be for the manufacturers to simply mark the foil side. Guess they 'lost that technology '. Thanks

[@JagStar]

They used to do it in the 50’s and 60’s, but the marking was often on the wrong side. Back then, they were done on an assembly line and the workers didn’t always pay attention when they were putting the jacket on. I’ve tested a lot of those old, blue Mallorys and they are marked wrong quite frequently. I’m not sure why they don’t do it today. I think that with modern automation, it should be easy and reliable. Thanks for the comment!

[@luminousfractal420]

factories set to dgaf mode. theyd have to shut down and fix all the areas the caps get mixed at (some random conveyers someplace.) lots of cost if your already set up. new factories....3million for an aligner machine.."they have oscilloscopes."

[@luminousfractal420]

so basically the shield isnt a shield...its a little antennae. your not shielding with the casing, your just pulling an external signal or your not. kind of the opposite to how its talked about. if theyd called them mini antennae to start with it all would have made perfect sense right away. that noise signal doesnt really make it through the cap mechanics and chemistry obviously, but it can be amplified by it in a negative way at the other end. you want the cap to cap it, not amplify it. thats definately going to make a mess of your audio.

[@commieslayer8218]

Martians invented the marsh mellows

[@JagStar]

😂😂😂😂 I think I need to bring back The Ego. I haven’t done anything with him for a year.