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Old 26th Nov 2020, 7:30 pm   #1
ChrisThomas
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Default Meaning of numbers of loops shown for coils in schematics

Possibly a daft question...but...
On the circuit diagram I have for my Bush VHF102, the various coils in the inductors have different numbers of loops - e.g. for the power transformer (photo of schematic attached), there are 10 loops on the primary side and 4 and 3 loops on the two secondaries, the first of which is centre-tapped. The different numbers of loops clearly isn't random, so must mean something - e.g. a proportion? My beginner's question is: what can be usefully determined from these numbers of schematic loops with regard to circuit function?
Many thanks - again!
Chris
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Old 26th Nov 2020, 7:43 pm   #2
deswradio
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Default Re: Meaning of numbers of loops shown for coils in schematics

I think that you can deduce very little from the number of loops. As far as I know, the number of loops is governed by artistic license so that the diagram looks "nice"!

Best wishes

Des
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Old 26th Nov 2020, 7:46 pm   #3
kalee20
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Default Re: Meaning of numbers of loops shown for coils in schematics

On a transformer in a diagram, I tend to use more loops where there are more turns. So, to show if a transformer is step-up or step-down, or, if more than one secondary, which produces the higher voltage.

But that's it. I don't with a standard loops-per-volt personal figure!
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Old 26th Nov 2020, 7:48 pm   #4
Simon Gittins
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Default Re: Meaning of numbers of loops shown for coils in schematics

It's usually arranged so that you can see if it is a step-up or step-down transformer but it's not in proportion to the extent that you can work out the ratio.
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Old 26th Nov 2020, 11:36 pm   #5
Terry_VK5TM
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Default Re: Meaning of numbers of loops shown for coils in schematics

I think the most you can deduce from the number of loops in a coil/transformer symbol is how much space there was on the drawing to fit it in.

There are no official standards on the number of loops that should represent something relating to coils/transformers that I know of (there are various standards relating to how they should be drawn, that a large proportion of the world ignores anyway).
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Old 27th Nov 2020, 2:22 am   #6
ThePillenwerfer
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Default Re: Meaning of numbers of loops shown for coils in schematics

The number of 'spikes' on resistors also varies. For instance Pye's own data for the P75 uses three, the Bush sheet for the DAC90a four and the Trader sheet for either shows seven.
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Old 27th Nov 2020, 4:53 pm   #7
ChrisThomas
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Default Re: Meaning of numbers of loops shown for coils in schematics

Thanks all - a shame the representation isn't more systematic! But there we go...I suppose there are limitations in drawing up schematics, especially more complex ones...
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Old 27th Nov 2020, 5:21 pm   #8
emeritus
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Default Re: Meaning of numbers of loops shown for coils in schematics

In the 1970's and '80's I was a Patent Examiner at the UK Patent Office. Most of my cases related to transistor circuits but it was sometimes necessary to search the files relating specifically to valves, and these included patents dating back to the early 1920's (under the older 1949 Patent Act, the examiner could only cite documents published in the preceding 50 years, so the older documents used to get weeded out). There was (and still is) no requirement to use any particular drawing convention, and I found numerous changes in the practices used by applicants from different countries at different times. In the inter-war period, the zig-zag symbol was sometimes used for transformer windings and inductors, resistors being represented by a square wave-like symbol. Other documents of the same era used the square wave symbol to represent non-inductive resistors. Germany often used an open box for resistors and a solid box for inductors. The US used the UK capacitor symbol for relay contacts, hence their use of a capacitor symbol with one straight plate and one curved plate. In the post-war era I found dozens of different transistor symbols with little consistency as to which is used for what, even in applications from the same company. One of my colleagues who had worked in the patent department of a private company before joining the PO, mentioned that one of his tasks had been to re-draw circuit diagrams to make them as obscure as possible: - there are at least six different ways of drawing a simple flip-flop consisting of a pair of cross-coupled NAND gates! Before I left I did start preparing a compendium of all the different semiconductor symbols I had met to assist my sucessor but only half-competed it.

The point is that, with circuitry, unless you are certain as to the drawing convention being used, you may need to refer to supporting documentation to fully understand a circuit diagram.

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Old 27th Nov 2020, 5:51 pm   #9
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Default Re: Meaning of numbers of loops shown for coils in schematics

Looking at the Bush schematic the OP posted in #1, I think his uncertainty is entirely understandable. That main secondary winding is clearly symmetrical around the centre-tap, so to show it as an asymmetrical winding is just sloppy draftsmanship, even if we can work out what's going on.

Mike

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Old 27th Nov 2020, 8:15 pm   #10
John M0GLN
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Default Re: Meaning of numbers of loops shown for coils in schematics

You don't always get loops these days, this is part of the power supply circuit for my Marantz NR1501 AV Receiver.

John
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Old 27th Nov 2020, 10:01 pm   #11
Herald1360
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Default Re: Meaning of numbers of loops shown for coils in schematics

Looks like you still get asymmetric centre taps too!
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Old 27th Nov 2020, 10:33 pm   #12
pmmunro
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Default Re: Meaning of numbers of loops shown for coils in schematics

When making drawings manually, I always followed the conventions outlined by Kalee and others; show the relative proportions of the windings but accept that more than that is impractical. I would agree that centre taps should be represented symetrically.

Now that most diagrams are drawn using CAD, it is important that they are drawn strictly to a grid, usually 2.5mm pitch with one in four dots visible. If this is not done, it's very difficult to join components up sucessfully. This imposes some awkward constraints on the the relative dimensions of components which might have to be stretched or compressed in one dimension to fit the grid, but one way to overcome this is to add 'lead-out' wires to the symbols so that the ends of the leads fit the grid.

PMM
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