How to make a shielded capacitor for a tube radio or amp.

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How to make a shielded capacitor for a tube radio or amp.
Those 3 legs on an old capacito may seem strange at first, but quite simple once you understand that they are actually shielded capacitors. These were used when they wanted to reduce noise pickup in high impedance sections of tube radios or amps.
Quite simple really, but very hard to get these days. Solution? make your own.
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15 фев 2017

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Комментарии : 67

@abeleballestri612 7 лет назад

As usual I have learned quite a lot how to shield a coupling capacitor if it must be shielded. Very practical and easy way of doing it. Thanks a lot.

@electronicsoldandnew 7 лет назад

+abele ballestri : glad you liked it.

@mikedevita5558 4 года назад

I tried it today. Works great.

@alfredneumann4692 5 лет назад

I have used coppersheet as a shield (was in the late 80s). I would isolate the groundpin also with a black shrinktube. Only for security. Your solution is clearly better the the original. Have to notice this :-)

@fakharvoice9215 4 года назад

Woooooooooooooooooooooooooooooooooooooooow.....Love 4rm PAKISTAN

@BKGoldDetecting 4 года назад

Thanks, this has been a great help. I am a just starting out in this hobby and have found your videos very informative. When I first found one if these capacitors in my radio it really confused me as to its purpose. In my case there was also a shielded wire to the pu which soldered time the same connection as the shielded capacitor.

@electronicsoldandnew 4 года назад

Glad to have helped.

@albertosequeira8759 3 месяца назад

Muito obrigado Sr . Caldeira! Excelente solução e que sem dúvida vou implementar! Grande abraço!

@electronicsoldandnew 3 месяца назад

Prazer 👍

@chrisschober3085 4 года назад

Many thanks, your video saved me many hours of investigation.

@electronicsoldandnew 4 года назад

My pleasure

@BKGoldDetecting 9 месяцев назад

Ive been using this method for a few years now but on my latest radio I tried something different. I took the paper off the old cap and the original foil is just loosely wrapped around the capacitor with the wire attached. I just cut it to width and wrapped it around my new capacitor, including the original wire and put a small dab of superglue to hold in place till the heat shrink was put in place. Very simple and looks very tidy.

@electronicsoldandnew 9 месяцев назад

That’s a good way to keep it looking more original 👍

@BKGoldDetecting 9 месяцев назад

@@electronicsoldandnew I would love to see you try this technique on one of your radios. :) Once you unroll the foil you just need to break off a small piece of the wax on the ends that holds the wire in place. Regards Kevin

@electronicsoldandnew 9 месяцев назад

It’s not something I have considered doing. The idea of making a radio look like it’s not been restored is useful if you really want to keep it absolutely visually original, but that’s not the goal in my restorations.

@dirkk82 5 лет назад

Thank you for showing this, I'm restoring my second radio and had also found one of these ero shielded caps had no idea what it was ! I will be sure to do the same to the replacement cap. Thanks again and cheers from Germany 😊

@electronicsoldandnew 5 лет назад

dirkk82 : You’re welcome. I was also a little puzzled the first time I came across one of them.

@dirkk82 5 лет назад

@@electronicsoldandnew i made a video on this subject with my own version of the replacement cap. i have included your video and channel in my description, i hope that's alright as i found this quite interesting and useful knowledge plus your camera has better zoom :-D

@electronicsoldandnew 5 лет назад

dirkk82 : absolutely no problem. I appreciate it. Thanks.

@davidtube9895 3 года назад

Thanks

@waynethompson8416 4 года назад

I have never heard of such caps before! Interesting! I think that if I ever make one like that, I will use different size braid from coax, black heat shrink for the ground wire, green shrink for the low impedance side wire, and red for the "hot" end wire. Since the copper braid will cover up the writing on the capacitor, I would type small print on paper, place that over the braid on the body of the capacitor, and then cover the paper with clear heat shrink so you could still read the value and voltage information. I would use wire to bind the larger braid on the body of the cap to the smaller braid on the lead. I think that would make it less lumpy that way.

@michvod 3 года назад

I restored few radios that had factory made shields around the capacitors. They were in tone circuit. They wrapped the capacitor with a thin foil of some kind of solderable metal (it tarnished a lot over the years). So the replacing was trivial, just desolder the shield and put some heat shrink around the new capacitor then resolder the old shield onto the new cap, and resolder the ground lead.

@electronicsoldandnew 3 года назад

👍

@DoRC 7 лет назад

very cool. I think I'll try this out.

@anthonybraga5649 4 года назад

Great idea Thanks for sharing

@electronicsoldandnew 4 года назад

Pleasure

@lelandclayton5462 7 лет назад

I've done this a few times with guitar amps. Mostly solid state but it still works. I just used Mag wire and put some HVAC tape over the cap. It really doesn't matter to cover the whole cap however to make sure you heatshrink the ends so you don't cause a short. You can create inductance if you wrap the wire around the cap. A friend of mine got a hold of some aluminum braid cable that he uses for shielding.

@electronicsoldandnew 7 лет назад

+Leland Clayton : this solution, or any similar one, is very rarely needed, but when it arises, you do what you have to. The aluminium braid is a good idea. In the tube guitar amps that I've designed and built, I usually design it so that any noise sensitive connection is wired with proper shielded cable, and the coupling component is connected very close to the end point, so this is not needed.

@dougroundup7315 6 лет назад

We all pretty much know that it is good practice to put the outside lead towards the lower impedance section to be coupled but I have never noticed shielded caps before. Certainly modern printed circuits have put these types of tricks to rest. Obviously as we explored higher and higher rf frequencies the need to shield became much more critical. Today with the proliferation of boutique guitar amp builders and the demand and widespread popularity of handwired point to point circuits, tag boards and turret board type construction this might be another tool in the quiver for those that continue to escalation of higher and higher gained amplifier circuits. This along with very careful lead dressing and placement might make the difference in a noisy or unstable high gain guitar amplifier, such as the various trainwreck or tweaker type curcuits.

$@luminousfractal420$

@luminousfractal420 4 месяца назад

2mm copper soldering wick for the wires, or maybe thin hobby tubing

@electronicsoldandnew 4 месяца назад

👍

@blitzroehre1807 4 года назад

Important point of note: There is an identical looking ERO cap with a third leg which is a combination of capacitor/resistor. David Tipton and myself nearly fell for this when we each restored a Nordmende Elektra just recently. He explains this exactly right at the beginning of his video here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-J1hm2DAmo20.html

@electronicsoldandnew 4 года назад

That’s right. It can really catch you out if you’re not careful. I also saw Dave’s video. I’m a fan of his channel.

@creative27feb Год назад

that Chocolate.😂

@rosshollinger8097 4 года назад

This will be very useful. Thanks for sharing this. Oh, and Dr. Frankenstein would be proud. :>D

@electronicsoldandnew 4 года назад

He was my varsity professor 😊 McGyver was in the same class.

@mark006868 7 лет назад

It could only be used as a short term solution as the galvanic reaction (also called bimetallic corrosion) between the alloy foil and the silver wire will fail at one point and it will no longer be shielded.

@electronicsoldandnew 7 лет назад

+Mark David : how short term? I wind the wire round quite a bit, so I hope it won't fail in my lifetime (and that I have a decent lifetime left).

@mark006868 7 лет назад

It all depends on how much the two metals react to each other and how they react.All it takes is a small reaction and it oxidizes or corrodes causing a bad connection and therefore a loss of shielding...however the actual corrosion in each metal is difficult to predict....but...Galvanic corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly and what the humidity level in any given location which will accelerate any reaction...A quick look at the Galvanic reaction chart shows us that Aluminum does not do well with most other metals. Although it may cost a bit more copper foil might be a better choice and could be soldered to the wire for a much better connection...so...If you live in a dry dessert you might get away without any issues.....and good luck with your lifetime....lol

@electronicsoldandnew 7 лет назад

Mark David : thank you for the explanation. Copper foil it is from now on.

@michaelfriedlander750 6 лет назад

Yeah he's right. You can't rely on aluminum connections to dissimilar metals. I'm going to use copper tape and solder to the copper, but I think I would rather use mu metal tape...or maybe put a braided shield over the whole thing.

@mtabernig 7 лет назад

c]Check the band at one end of the cap. it shows the shielded end,

@electronicsoldandnew 7 лет назад

mtabernig : good point. Thanks for pointing that out. I forgot to mention it.

@DoRC 7 лет назад

mtabernig most non electrolytics don't have any polarity indication.

@mtabernig 7 лет назад

well not true....the new orange Epoxy do...and some of other types also do the very small ceramic type do not but in that case do not need shield. Obrigado.

@DoRC 7 лет назад

mtabernig hmm. most orange drops I use have no marking. guess I'm using the wrong brand:)

@scottw6831 5 лет назад

@@mtabernig That band isn't always correct - see the Mr. Carlson's Lab video on determining outside foil layer ----> ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-BnR_DLd1PDI.html

@trebushett2079 3 года назад

Great idea - not so great an execution !

@electronicsoldandnew 3 года назад

noted 😊

@bradishear9369 Год назад

I was trying to test the voltage of a small electric mini fridge fan motor. I accidentally touched the outside top of a power supply can capacitor to ground via my hand. It shocked me good. So out of curiosity I checked the voltage between the top of the can to the body of the fridge and it was 122 volts. I checked the next can over and it was 122v as well. This does not sound right. Do I need to take this in and have a service center check the capacitors? 😢

@electronicsoldandnew Год назад

I would say so.

@RandomsFandom 6 лет назад

I woulda used some sort of nail polish to join the shrink tube to the cap

@melissahermsen5630 4 года назад

Sorry, but shielding the wires to and from the cap is overkill. It may even prove a shot in the foot. It only takes a little bend on the connecting leads and a solder job taking a bit too long for the green insulation to melt through and produce a short between cap leads and the added shielding foil. Make that short an intermittent one and you are in for an hour long hunt. If you really need to shield the wires too use a heat resistant tubing made from woven glass fibres as insulation/separation! Easiest way to shield tubular film caps is to cut a flat piece off of a tin can, roll it to fit the diameter of the cap very snugly, trim it to circumference plus overlap, solder on a wire and shove it over the cap. A final wrap in shrink tubing cut to the length of the cap plus a bit of overlap will hold your shield in place. There is no need to solder the selfmade wrap around shield into a tube, as long as the circumference overlaps. Yeez, this is not rocket science!

@electronicsoldandnew 4 года назад

You’re right. It’s not rocket science, so I do it my way, as I’ve done numerous times with no hassles, and you do it yours. That way, both of us are happy :)

@waynegram8907 2 года назад

How can you tell when looking at a schematic which sections or stages are high impedance to use the shielded capacitor? I'm not even sure how to use a shield capacitor for coupling caps, decoupling bypass caps or what? EE engineers have told me that using LOW capacitance shielded cables in amplifiers makes the low capacitance cable very microphonic when you're tapping it with a wooden chop stick in high gain circuits but High capacitance shielded cables used in amplifiers are NOT microphonic, any reasons why lower capacitance shielded cables are more microphonic compared to high capacitance shielded cables?

@electronicsoldandnew 2 года назад

If the connection is to a high impedance pin, like the grid, then capacitance will, through the miller effect, create a low pass filter. The higher the capacitance, the lower the frequency cutoff point. However, The lengths of cable one uses in an amp should not be large enough for this to be an issue.

@waynegram8907 2 года назад

@@electronicsoldandnew You put the OUTER foil terminal of the capacitor to the previous stage output of the tube and the INNER foil terminal of the capacitor to the GRID pin tube to the next following stage? But where does the capacitors shielding connect to?

@DeeegerD 5 лет назад

I'd just use the outter foil to ground or lowest potential point. That should be fine.

@electronicsoldandnew 5 лет назад

It’s better than the other way around, but not a complete shield. I personally don’t think most situations warrant this effort, unless oscillations result from failing to do so.

@noelwilliams3224 7 лет назад

Is an electrolytic capacitor already shielded?

@electronicsoldandnew 7 лет назад

+Noel Williams : the negative terminal is usually connected to the outside "shield", but since you don't always have that connected to ground, I guess you would still get noise pickup.

@noelwilliams3224 7 лет назад

THANKS! You have been a tremendous help! Now, (hate to keep bothering you) what is the name of sleeve that goes over foil and cap? You said it was (big-o-it-try)?

@electronicsoldandnew 7 лет назад

+Noel Williams : it is heatshrink.

@hestheMaster 4 года назад

This kind of capacitor was used in many RCA radios in the 1940s to suppress the harmonic frequencies that would occur in AM band from maritime AM broadcasts back in the day , They would overpower the reception of a station you were listening to especially if you lived near the seaside. Of course after WWII the maritime transmissions went to FM broadcasting and thusly no need for them in the USA in radios after that happened. Not sure if that is why non USA radios have them. If you encounter one in a restoration you could cover the capacitor with a braiding just for effect if you live in America ,that is!

@electronicsoldandnew 4 года назад

Thanks for the info. I certainly did not know that.

@electronicsoldandnew 4 года назад

Thanks for the info. I certainly did not know that.

@hestheMaster 4 года назад

@@electronicsoldandnew Mr. Carlson said of those many RCA radios that they put those types of capacitors inside the chassis to keep down hum when it went from the volume control to the center of the radio. I 'll defer to him since I only picked up the info from my grandfather long ago and he only saw them in a few RCA radios!