Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Jun Thu 21, 2018 5:10 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 14 posts ] 
Author Message
 Post subject: Shielded Film/Foil/Paper Capacitors (with three lead wires)
PostPosted: Feb Sun 25, 2018 5:31 am 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
As I was recapping some radios I encountered some multi section paper capacitors.

I totally understand how to recap multi section electrolytic caps, but there is one thing unclear to me if the multi section cap is a paper cap.

I've Googled "multi section paper capacitors" left and right but I only find information on multi section electrolytic caps.

On the image we see a cap that I pulled out, labeled simply .025uF. I recapped as shown on the drawing over the picture.

Attachment:
IMG_0420.jpg
IMG_0420.jpg [ 126.99 KiB | Viewed 407 times ]


If this was a multi section ceramic disc capacitor the recapping would be easy to understand. But this is a rolled up film cap, so should there be a third cap between A and B points?

I can best explain my dilemma with the following drawing.

Attachment:
multicap.jpg
multicap.jpg [ 64.86 KiB | Viewed 407 times ]


If I think of this cap as a roll, I can clearly imagine an active area (colored yellow) between the A and the B foils. In fact, when I measure the discarded capacitor I also measure capacitance between the A and B leads. But the values on the old cap are very much off, so the measurements are inconclusive.

So, should there be a third cap between A and B points?

Thanks...


Last edited by Adinol on Feb Sun 25, 2018 5:52 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 5:42 am 
Member
User avatar

Joined: May Tue 05, 2009 2:30 am
Posts: 1454
Location: Saskatchewan, Canada
German? I think A & B is a normal cap, and the small lead off to the side is just a shield.

_________________
Another day older and deeper in debt.


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 5:49 am 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 22337
Location: Annapolis, MD
How does this part appear on the schematic?

One clue would be to measure the capacitance between all of the three possible pairs. ( one lead not connected for each measurement)

_________________
-Mark http://pixellany.com

"It's always something". --Gilda Radner (1946 - 1989)


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 5:53 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 32700
Location: Maryland 20709, USA
That's a European capacitor.
It really doesn't matter since their electrons work just like ours.

There are various ways of making multi-section paper caps.
One that has not been mentioned is splitting one foil at the middle with part going to each end lead.
The common lead (usually ground) goes to the other foil, which runs the full length of the cap.

- Leigh

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 5:56 am 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
marko wrote:
German? I think A & B is a normal cap, and the small lead off to the side is just a shield.


Oh, I see. So I recapped incorrectly. I guess I should just wrap a regular film cap in a foil and ground that foil.

You are correct. I am encountering those caps in three German radios.

pixellany wrote:
How does this part appear on the schematic?


It was unclear to me until marko said it was a shielded cap. Now I see the schematic shows a cap surrounded by a box drawn as dashed lines. What marko said makes sense now.

pixellany wrote:
One clue would be to measure the capacitance between all of the three possible pairs.


I do measure capacitance between all pairs, but the values are all over the place. I can't get consistent values between two caps that are supposed to be the same.

I guess at this point I'll go with marko's recommendation and just wrap a new film cap in a foil and shield it. Or are there any more elegant solutions?

Thanks...


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 5:59 am 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
Leigh wrote:
There are various ways of making multi-section paper caps.
One that has not been mentioned is splitting one foil at the middle with part going to each end lead.
The common lead (usually ground) goes to the other foil, which runs the full length of the cap.


I didn't think of that. But I think between the schematic and what marko says, it's probably not a multi section film cap, after all.


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 6:01 am 
Member
User avatar

Joined: May Tue 05, 2009 2:30 am
Posts: 1454
Location: Saskatchewan, Canada
I haven't been in a german set lately (or any radios for that matter) but I remember seeing these in some I capped in the past. Usually only a couple spots, I guess low signal, HF, areas? I forget. Maybe post a schematic here, so we could see if a multi section would make sense, or if shielded is more logical.

I guess if you're extra curious you could try taking it apart too, that should reveal the secret.

_________________
Another day older and deeper in debt.


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 6:03 am 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
Here is how one of the schematics show three of those caps.

Attachment:
wrapped-caps.png
wrapped-caps.png [ 58.21 KiB | Viewed 395 times ]


I guess it's like a cap inside its own grounded enclosure.

marko wrote:
I guess if you're extra curious you could try taking it apart too, that should reveal the secret.


Good idea! I think I might just do that.


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 6:17 am 
Member
User avatar

Joined: May Tue 05, 2009 2:30 am
Posts: 1454
Location: Saskatchewan, Canada
jogging my memory a little, looking a few schematics, Maybe they used them more around the tone controls and low level audio parts.

in this schema: https://nohm.eu/schematics/Nordmende/Ca ... 6%20RG.png

you can see a couple on the grids of the two triodes in the audio portion (EABC80, etc). It's drawn a bit more clearly as a grounded shield there.


edit: I wrote gate instead of grid... my I'm getting rusty with this hollow state stuff!

_________________
Another day older and deeper in debt.


Last edited by marko on Feb Sun 25, 2018 6:19 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 6:18 am 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
Mystery solved.

Attachment:
IMG_0592.jpg
IMG_0592.jpg [ 43.84 KiB | Viewed 393 times ]


It's a cap wrapped in foil as a grounded enclosure.

Thanks....


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 1:48 pm 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 22337
Location: Annapolis, MD
Adinol wrote:

I guess at this point I'll go with marko's recommendation and just wrap a new film cap in a foil and shield it. Or are there any more elegant solutions?

Thanks...

I make them using braid for the shield, then shrink-fit on the outside.

_________________
-Mark http://pixellany.com

"It's always something". --Gilda Radner (1946 - 1989)


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 2:51 pm 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
pixellany wrote:
I make them using braid for the shield, then shrink-fit on the outside.


Do you mean, to just strip some braided wire and shrink fit it?

I was thinking of using a self adhesive copper sheet and solder on a lead. If I can find the piece of copper sheet that I know I stashed somewhere.


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 3:06 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4443
Location: Perrysburg, OH, U.S.A.
Adinol wrote:
pixellany wrote:
I make them using braid for the shield, then shrink-fit on the outside.


Do you mean, to just strip some braided wire and shrink fit it?

I was thinking of using a self adhesive copper sheet and solder on a lead. If I can find the piece of copper sheet that I know I stashed somewhere.

If you can't find it, McMaster-Carr has it: https://www.mcmaster.com/#foil-tape/=1bq205x
They also have the same thing with an electrically conductive adhesive, but if you overlap the type above a little it will work just fine.
John

_________________
“Never attribute to malice that which can be adequately explained by stupidity.”
― R. A. Heinlein


Top
 Profile  
 
 Post subject: Re: Multi Section Paper Capacitors
PostPosted: Feb Sun 25, 2018 5:51 pm 
Member
User avatar

Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
Here! Done!

Attachment:
IMG_0596.jpg
IMG_0596.jpg [ 34.33 KiB | Viewed 335 times ]


Attachment:
IMG_0597.jpg
IMG_0597.jpg [ 31.3 KiB | Viewed 335 times ]


I flattened a scrap component lead wire and soldered to the copper shield. The copper shield is overlapping the capacitor's body (just like the old Germans did it) and I filled those cavities with epoxy (just like they did it).

After the shrink wrapping I took the time to write a label with the value .025u/630V and even wrote "shielded capacitor" on the label, so the next guy that'll be recapping won't have to ask the same question on a forum.

I also should edit the title, since this post is probably going to help someone in the future.

Thank you guys... (especially marko)...


Top
 Profile  
 
Post New Topic Post Reply  [ 14 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: engineer, Leigh and 5 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB