Design & Build a capacitor outer-foil detector for restoring vintage audio & radio gear

Only $5 for 10 PCBs and every new member get $5 bonus. + Express 24 hour / 48 hour service on www.pcbway.com/ ➠ ➠ ➠ Respecting foil capacitor 'polarity' in the restoration of vintage electronics gear is a much-debated topic these days. Some say it's crucial, while others say that it makes no difference as modern capacitors don't have the same issues as those of old.
While I personally am a little on the fence on the subject, I always do a test to determine which lead is connected to the capacitor's outer foil. Can't hurt, right? The oscilloscope has been my tool of choice to date.
The process is easy, but a little cumbersome, so I decided to design and build a self-contained device to do the identification for me. It also represented an opportunity to build it as another of my 'under the shelf' units, which are incredibly useful. So, if this sort of thing interest you, stick around and enjoy the video.
If you wish to order your own PCBs from PCBWay, the link is below:
➠➠ www.pcbway.com/project/sharep...
Other Creators mentioned in this video:
‪@MrCarlsonsLab‬
🙏 Want to support the channel? ●●●●●●
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#tuberadios #antiqueradio #radiorestoration
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[@stevegreen5358]

I just found your channel after watching dozens of Mr Carlson's videos, and I joined your Patreon channel immediately. I don't want to make my own PCBs and I don't want to use surface mount components, so I am so glad you use through-hole components and make the Gerbers available. PCBWay's pricing is ridiculously cheap, so I will make some of your projects very soon.

[@electronicsoldandnew]

Welcome to the channel and for your support. I really appreciate it. I prefer to make the Gerbers available as for some people the shipping can be quite costly. Personally I actually like SMD, but many have problems with it, so k normally opt for through-hole versions as it’s more generally preferred. If you have any questions, feel free to ask through patreon. I’ll be happy to help where I can.

[@Patrick-rd9qo]

Appreciate the detailed and clear walk through of the design process, thanks for sharing!

[@electronicsoldandnew]

My pleasure

[@multicyclist]

I made one years ago with just a small aluminum box, a toggle switch, a speaker spring clip to hold the capacitor, and a BNC connector to hook to a scope. The switch is mounted parallel to the capacitor. Simply hold the capacitor with one hand and flip the switchback and forth while looking at the scope, and stop when it reads the highest. The switch handle automatically points to the foil side. I put a piece of plastic tubing over the switch handle to insulate it. Simple and works well. So well in fact that I don't have the need for anything else.

[@electronicsoldandnew]

👍 if it works, why change 😊

[@radio-ged4626]

It's quite generous of you to share the build info of test equipment you design. But it is in the spirit of the community that follow you. Thank you for sharing I'm sure I will build this at some stage.

[@electronicsoldandnew]

I like the community feel of this channel, so it’s a pleasure to give back whatever I can.

[@haraldlonn898]

The first op amp at the dut is not needed. I like it and have own ideas. Thanks for your great videos.

[@electronicsoldandnew]

Pleasure

[@ralphjarmain3851]

Excellent piece of test gear. If you didn't already have the relays, you could use analogue switches (some have very low on resistances and draw uA but you would have to fiddle with the supplies a bit). In my head I have a mod that would induce 50Hz into the test cap, rather than having to touch it, but that would be version 100.

[@electronicsoldandnew]

That’s actually quite easy to do. It doesn’t have to be 50Hz. You can add a small oscillator (200 - 1000 Hz) and have it drive a small coil near the cap.

[@DavidTipton101]

A fine project Manuel, you are a smart man 👍🙂

[@electronicsoldandnew]

Thank you Dave. You’re smarter … you take cruises 😊

[@haraldlonn898]

4066 is a great relay replacement. Thanks for great videos.

[@MarcelHuguenin]

Congratulations Manuel with another interesting project and thank you for your class on the design.

[@electronicsoldandnew]

My pleasure

[@anandarochisha]

Sweet project, Manuel.

[@electronicsoldandnew]

👍

[@petersdelucaaa2vg306]

This is a very useful tool. Thanks for the excellent explanation about how it works and how you designed it. Most importantly, thank you for sharing the PCBs. They are on order.

[@electronicsoldandnew]

👍

[@mackfisher4487]

Brilliant innovation

[@electronicsoldandnew]

Thanks 👍

[@mostlyoldthings]

Excellent lesson in circuit design Manuel, very interesting to learn more about op amps which I knew only a little about, thanks vey much. Nice overall design of the foil side tester too!

[@electronicsoldandnew]

👍

[@MrElectrowhiz]

Now you need to come up with a electrolytic polarity tester. I have found some capacitors that were marked wrong, mainly tantalums.

[@timolubeck988]

Tantals have the positive marked, other electrolytics the negative.

[@jasonatkin6787]

Just wanted to shout out that I enjoy your equipment builds immensely. I've built the Zener Diode Voltage Tester and it's one of my favorite pieces of home-brew test equipment. Will be building the capacitance leakage tester next as soon as a suitable project box happens my way. This one will probably follow.

[@electronicsoldandnew]

👍

[@rodsradios]

Nice One Manuel, I've ordered the PCB's.

[@electronicsoldandnew]

👍

[@JonRig]

Great project!! Love it!!! I really appreciate you sharing the details and thinking behind what you have done. I only understood op amps at a very superficial level so this has given me a better understanding of the (creative!) ways in which they can be used. Great learning and a really neat tool too! I'm at the fingering them on the scope and black marker pen stage! 😁

[@electronicsoldandnew]

That’s what I used to do, and got tired of it … and … any chance I get to extend my “under the shelf” family … 😊

[@harrilumme1875]

Nice timing! I had just started the same project and ended up with pretty much identical design. (I still thought I'd use the 555 timer). Now I can use ready-made PCB's! Thanks Manuel.

[@electronicsoldandnew]

Pleasure 😊

[@EsotericArctos]

I made Mr Carlson's version of this detector. I'll have to have a look at yours and see the differences. I am always curious about how different peoples minds approach things and the different approaches used for the same thing :). Thank you so much for bringing these designs to us. It's appreciated more than you know.

[@electronicsoldandnew]

Always a pleasure 👍

[@haraldlonn898]

Sorry you got the first op amp wrong. Still a great video. Thanks.

[@electronicsoldandnew]

👍

[@InssiAjaton]

Instead of building your own 4-step comparator, you might have tried LM3914 that provides 10 steps with the divider network already built in. It would have provided finer steps and/or wider range. Of course, it would be a bit more expensive than your quad op-amp and also the 6 extra LEDs would add some cost. Also, you could benefit from making your buffer stage sort of logarithmic with just one additional diode and resistor or two. That would expand the range and reduce the need for adjustment of the potentiometer. From your presentation, I conclude that you would be fully up to the challenge.

[@davidmann8504]

If you want logrithmic you could also try the LM3915 IC (3dB per step)

[@electronicsoldandnew]

Had that planned initially, but then decided that it was not necessary for the purpose here. Also … drilling lots of holes for the LEDs is a pain 😊

[@ivolol]

I declare myself 'one of the few?' that absolutely live for seeing the schematic design and decisions in these. That's the magic, understanding the circuit so I can go make my own! edit: I would think about making a "range sensitivity" to select between large or small voltage differences, so could look at caps with large or small variations. So it could switch between using a 22k pot and a 100k pot for instance, before going to the 1k dividers

[@electronicsoldandnew]

Always useful as it cements our knowledge and raises new questions 😊

[@BJcanal270]

Very interesting. I am waiting for you to build a Milli ohm meter gadget 🙏

[@robert-nv1qn]

Sir, I may be wrong but in the beginning I think you have incorrectly labeled the non-inverting op-amps. I think the input should go to the non-inverting (+) input and the output connected to the inverting (-) input. Again, I might be wrong.

[@electronicsoldandnew]

You’re probably right 😊 I sometimes do that. Fortunately the schematic that results in the pcb is correct. Thanks

[@tubeDude48]

A new orange drop may have a partial band on it, but they need to be checked since that band means nothing! I'm sure you agree. A 1N914 will work as well. To make it solid-state, you could use a CD4066, or 74HC4066. Another E O&N original project! Nice work. 👍

[@electronicsoldandnew]

Thanks 🙏

[@JesusIsLordofMybeing]

Awesome project!!! Thanks so much for sharing and I already received my pcb's. Can I respectfully ask if you can share a list of all the latest part numbers you used for this build? Thank you so much

[@electronicsoldandnew]

I’m afraid I didn’t draw up a parts list. The parts can be determined from the schematic and the videos.

[@michvod]

Nice one! I am interested how much difference it actually makes if you put capacitor in wrong way. Would be interesting to recap a radio with all the capacitors backwards, then turn them around one by one and check the hum levels. I usually use an oscilloscope to check the capacitor foil side, but I noticed that sometimes one series of capacitors has the difference so minor, that I can't see it on a scope, I usually don't bother then, as even in practice, the improvement would be really small. I had this happen especially on lower value capacitors (1nF-10nF). Also I don't think this works on ceramic caps, as they are built mostly completely symmetrically. But perhaps you also try it, as I do sometimes use ceramic capacitors to replace paper, especially on not so critical parts like AVC line, etc.

[@Vaionko]

kzbin.info/www/bejne/h4XEipqKbMpobNk XrayTonyB did a video doing pretty much what you describe

[@electronicsoldandnew]

👍

[@mddawson1]

Thank you for sharing this design. Is there a parts listing available?

[@electronicsoldandnew]

Afraid not. You can get that directly from the schematic.

[@robnic52]

What scope settings show this effect best please? Really interesting video. If you cover this later, apologies. Should have waited until the end. :)

[@electronicsoldandnew]

You’ve got to set the vertical scale to about 5mV, and set it to read a 50Hz signal.

[@sanosanbaby]

please remind me, why do you want to know the foil side? UPD: Thank you for the video! It's awesome

[@electronicsoldandnew]

Old caps were marked so that foil side was connected the low impedance side to reduce noise. There are many articles on the web about this issue.

[@hartzellwr]

What are the specs for the LEDs used in this project. Sorry if this has been covered elsewhere. Do I need 5 volt or would a lesser voltage rating on the LED work just as well? Great project and thanks for sharing!

[@electronicsoldandnew]

Normal 3mm LEDs. The dropping resistor takes care of the actual voltage applied.

[@Michlag]

Manuel, please add in the description what cap side goes where... Whether foil side goes to the high Z path or viceversa... I always forget this!

[@electronicsoldandnew]

Foil side goes to low Z

[@paulperano9236]

Nice job. Keep this up and you'll need another shelf ! I'm giving a talk about OpAmps to my vintage radio society in a month or two. May I use your circuit diagram as an example ? It covers about 4 different uses for OpAmps. I managed to track down one of the earliest iterations of an OpAmp - the 'Gap/R Model K2-W' Google that and have a chuckle.

[@electronicsoldandnew]

Sure, use it by all means.

[@paulperano9236]

Cheers. Will also put in a promo for your channel too 🙂

[@electronicsoldandnew]

Thanks. I appreciate it.

[@harrystevens3885]

Like the gentleman says you just need a toggle switch............Plus there is a guy on KZbin that restored the same radio twice placing the modern capacitors both ways round and no noise difference was noticeable. Interesting project though.

[@electronicsoldandnew]

Yes, Xraytonyb.

[@Michlag]

Manuel, what tool do you use to bend the white steel covers? Hammer and bench?

[@electronicsoldandnew]

No, these are aluminium elements (6.5x6.5cm) that I had part of one side cut to give me access to the top and create the lip to hang on my rail.

[@Michlag]

@@electronicsoldandnew didn't understand however thank you and my compliments!

[@davesage9190]

Manuel: I just ordered the pcb's and selected to donate 10% to you. I also built your capacitor leakage tester. Another great project. Thanks. BTW would you have a final schematic with BOM I can download for this project? I like to keep all the info in one directory. I think for the leakage tester I did a screen grab of the schematic. Not ideal. Maybe I missed it somewhere. Thanks

[@electronicsoldandnew]

The schematic can be downloaded from the pcbway share page. I don’t have a BOM, I’m afraid .

[@davesage9190]

@@electronicsoldandnew Ok. I guess I missed it there. I saw the Gerber download though. EDIT: Found it - But schematic doesn't have the part number for the opamps nor the relay. There was no "link below" for the relay. Save me going through the video again. Can you give me the part numbers. Thanks

[@electronicsoldandnew]

Opamps are TL074, and the relay is a TQ2-12V

[@davesage9190]

@@electronicsoldandnew Great. Thanks

[@jonka1]

What about testing surface mount caps? Would it be worth making a jig?

[@electronicsoldandnew]

Nope. SMD caps are not made of rolled foils, so the effect would be zero.

[@eddys.3524]

Nice idea... but wouldn't it be an option to use an electronic switch controled by an oscillator to switch capacitor sides and the (single led) readout? the only thing you'd have to do is to adjust sensitivity. When only one led burns, that's the "wrong side of the Cap. BTW : add a (10k to 100k) resistor limiting the input current for the clamping diodes, doesn't influence the opamp too much because it has a FET input.

[@electronicsoldandnew]

I don’t like the auto-flip idea as I prefer to have more control over the process.

[@BJcanal270]

​@electronicsoldandnewI wouldn't add anything to your tester. Is perfect!!

[@electronicsoldandnew]

👍

[@Michlag]

Please Manuel, would you tell us the names of opamps used, and the relay? Trying to compile a BOM

[@electronicsoldandnew]

I used TL074

[@electronicsoldandnew]

Relay: TQ2-12V

[@Michlag]

@@electronicsoldandnew all of them?

[@electronicsoldandnew]

One relay, and two opamps (quad)

[@Michlag]

@@electronicsoldandnew Manu, please, would you remember the Gerbers for the stepped attenuator? Thank you!

[@Michlag]

Hey Maestro, however i think it makes no difference on old tube radio sets (no hifi in there), this might please some audiophiles (read audiophools 😂), yet I'll be building this for sake of curiosity on my 300b, gm70, tube phono preamp and other realizations... These miniatures you show every now and then are small treasures😊 ah, one thing more for the lazy like me, did you compile a BOM for the project? And never forget, electronics old and new you are good at restoring old radios and alignment of old radios, my friend 😂😂😂

[@electronicsoldandnew]

No BOM 😊 and… won’t forget that either 😊

[@Michlag]

@@electronicsoldandnew however, you've mail, for the Gerbers of the stepped attenuator, last version... Thanks 👍

[@electronicsoldandnew]

👍

[@robert-nv1qn]

apologies, I see the actual full schematic reflects changes. I "jumped the gun"

[@snakezdewiggle6084]

Most of the individuals who think they have discovered Free Energy, are, in fact, finding this phenomenon with their 5$ DMM. This project, while a useful tool for some, is somewhat redundant. I simply hold the Cap lead in one hand, and the MM lead in the other. But. To the ppl out there, learning, just now getting into Electronics. This is one circuit you must build. Breadboarding it at home will introduce you to the freakin' insane world of Op-Amps. Good, Bad, or otherwise, they are in every device you own.