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Author Topic: Vintage schematic symbol claification  (Read 3257 times)
KE8HAG
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« on: April 07, 2018, 01:39:20 PM »

I have an old vintage schematic for a vintage Hallicrafters receiver I'm attempting to repair and a bit confused about the capacitor symbols being used. All of the capacitors in this schematic, except variables, have the same symbol, an upside down "T" with the arched "T" below it, and no indicator, even in the PS. Obviously, the PS caps would be polarized but don't show a "+"  on the upside down "T".

My question. Is it safe to assume on these old schematics that any low value capacitors below 1 uf is not electrolytic and have no polarization.?

Thanks
Al
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W9FIB
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« Reply #1 on: April 07, 2018, 01:49:50 PM »

Personally, I would look at the schematic and see what is feeding each side of the cap. Especially to see if it is + or -. Assuming to much causes smoke to leak out of parts. Or even a possible shock hazard.

Even today, some companies are not careful in schematic creation and use generic symbols that don't tell the full story.
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73, Stan
Wisdom is knowledge you gain after you know it all.
AC5UP
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« Reply #2 on: April 07, 2018, 02:03:03 PM »

IIRC the curved side of the symbol indicates the outside foil of a tubular condenser which is typically installed closer to ground...  In the case of a variable condenser the curved line indicates the rotor.  Straight line the stator.  Hot Side  -|(-  Ground Side  (as in closer to ground, not necessarily at ground).

Do not assume anything less than 1uF is not polarized, although small value electrolytics are rare in hollow state designs.
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W9FIB
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« Reply #3 on: April 07, 2018, 02:03:33 PM »

IIRC the curved side of the symbol indicates the outside foil of a tubular condenser which is typically installed closer to ground.......

Hot Side  -|(-  Ground Side  (as in closer to ground, not necessarily at ground)

Do not assume anything less than 1uF is not polarized, although small value electrolytics are rare.

You are correct except all too often schematics are not drawn by electrically knowledgeable people and little things like that overlooked in the checking process and published with errors. I have seen this many times from many companies.
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73, Stan
Wisdom is knowledge you gain after you know it all.
KAPT4560
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« Reply #4 on: April 07, 2018, 02:04:41 PM »

 I always thought that the curved element indicated the common, ground or 'shield' side.
 Not necessarily polarized plus or minus, but for orientation indication.
 The same symbol with an arrow through it would be a variable cap:
 https://electronicspost.com/wp-content/uploads/2015/10/capacitor-symbol.png
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AA4PB
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« Reply #5 on: April 07, 2018, 02:05:40 PM »

Yes, it's the outside foil. The purpose is not polarization, but rather improved shielding. If the outside foil is connected to the side closer to ground then it helps to shield the capacitor's inner foil from coupling to other circuitry.
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Bob  AA4PB
Garrisonville, VA
KE8HAG
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« Reply #6 on: April 07, 2018, 04:18:24 PM »

Personally, I would look at the schematic and see what is feeding each side of the cap. Especially to see if it is + or -. Assuming to much causes smoke to leak out of parts. Or even a possible shock hazard.

Even today, some companies are not careful in schematic creation and use generic symbols that don't tell the full story.

 Looking at the schematic and looking at the circuit is what prompted me to ask. What I'm seeing in the circuit doesn't quite jive with the schematic symbol.
 Grin Embarrassed Yea....assuming is dangerous and potentially deadly, me know.


IIRC the curved side of the symbol indicates the outside foil of a tubular condenser which is typically installed closer to ground...  In the case of a variable condenser the curved line indicates the rotor.  Straight line the stator.  Hot Side  -|(-  Ground Side  (as in closer to ground, not necessarily at ground).

Do not assume anything less than 1uF is not polarized, although small value electrolytics are rare in hollow state designs.

Thanks

Didn't know how to make the symbol  -l(-  using the keyboard. But do now. Learned about the foil end on tubular condensers a while back.




I like learning and you kind people have shed light to a question I had. I'm very grateful for the advise and time you took to share your knowledge with me.

Much appreciated.

Al
73
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AC2EU
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« Reply #7 on: April 07, 2018, 05:04:32 PM »

Back in those days, a 1uf would probably be an electrolytic. A 1 uf non polar would have been HUGE.
Now a days , not so much. When in doubt, look and see what's there...
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KB2WIG
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« Reply #8 on: April 07, 2018, 06:58:40 PM »



What radio??

klc
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KE8HAG
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« Reply #9 on: April 08, 2018, 02:55:49 AM »



What radio??

klc

Hallicrafters S-53a
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G3RZP
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« Reply #10 on: April 08, 2018, 04:32:33 AM »

A 0.5 mFd  500 volt paper cap was around 1.5 to 2 inches long and bout 1 to 1.25 inches in diameter. Coated in wax, and normally leaky within two or three years of manufacture.....2 microfarad 250 volt were often in a metal can about 2 inches high, 1.5 wide and 5/8 inch thick, with terminals on the top. They tended to be pretty well sealed and didn't go leaky - at least, for anything up to 60 or more years.

You will often find that the paper caps had a coloured line - usually black - around them towards one end - that indicated the outside foil end. Similar plastic film caps could have a white line if they had a dark epoxy body colour.

There were electrolytics down to about 1 microfarad, but they weren't that common. The usual lower limit was 5 or 10 microfarad.
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WA3SKN
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« Reply #11 on: April 08, 2018, 04:54:59 AM »

That symbol indicates a capacitor.  I would not assume anything else.
Conventions were not followed very well back then.
73s

-Mike.
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KB2WIG
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« Reply #12 on: April 08, 2018, 06:48:55 AM »



You may find the following link usefull

http://bama.edebris.com/manuals/hallicra/s53a/


This schematic looks " normal ".

KLC
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WB4SPT
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« Reply #13 on: April 11, 2018, 10:33:23 AM »



You may find the following link usefull

http://bama.edebris.com/manuals/hallicra/s53a/


This schematic looks " normal ".

KLC

Wow, that's a clean looking schematic, apparently done in 1952.   Do you suppose that was hand drawn using templates?? 
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KB2WIG
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« Reply #14 on: April 11, 2018, 07:53:29 PM »


I don't know, I'd assume so......

My 'mechanical drawing' class didn't allow templates to be used. Everything was to be 'free hand' using the appropriate instruments. I never could never draw using drawing pens. Check this out.

http://www.daube.ch/docu/glossary/drawingtools.html

Back when I was ........

The 'lead' in the pencils was something like 1/8 inch thick, and had to be turned down to use. My first drawing submitted to the proff was graded C-.  The drawing measurements were correct, dimensioning, layout was OK. Why such a low grade??  He put my drawing on a light table; it looked like crap, the line thickness and density were not consistent, some lines were smudged. To me, it was a qualified OK, but to the Proff, it was a C-. I was a bit embarrassed when he placed the drawing on the light table. One more reason I'm not an engineer.

But I still find orthographic drawing useful.

klc
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