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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 10th Sep 2020, 2:08 pm   #61
kalee20
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Default Re: Grey beards and boffins; what do see when you see a circuit.

Quote:
Originally Posted by G6Tanuki View Post
Printing the full specification of each part on the diagram is not really possible - yes you can print "10nF" next to a capacitor but you still need to refer back to the parts-list to get the voltage-rating and construction/dielectric-type.
You need the full spec if you're making it or repairing it - but answering the topic question, if the primary value is present on the circuit diagram (your 10nF) then I know what I'm looking at, and roughly the circuit's function.

Any more than that, and the diagram gets cluttered with Too Much Information!

And valve types give a clue too - seeing a diagram of a simple-looking circuit with a few coils and a directly-heated triode, with 'DC90' alongside the triode, is going to have a very different circuit function than one with a similar arrangement of coils 'PX4' alongside the triode. The first could be a portable VHF RF amplifier, the second an AF output stage.
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Old 11th Sep 2020, 11:08 am   #62
David Simpson
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Default Re: Grey beards and boffins; what do see when you see a circuit.

Andy originally stated that he would like to improve his understanding of circuit diagrams.
Military spec & high end test equipment's circuit diagrams usually reveal a wealth of info on component size, rating, etc. Many also include an x & y reference around the edge of the diagram.
However, simple domestic radio's diagrams often omit valve electrode pin numbers, HT values, transformer winding's voltages, etc. I would encourage Andy & other folk to add these details in as their work on a radio progresses. This would help other folk in the future who seek diagrams. With a c/d blown up to A3, if there is space, I often draw-in several circles representing the underside of valve holders & write in pin numbers & corresponding details.
Circuit diagrams are really just a theoretical technical guide, and in reality factory construction folk often connected components in a non-sequential manner. I.e. - - effing higgledy piggledy in other words.

Regards, David
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Old 11th Sep 2020, 12:04 pm   #63
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Default Re: Grey beards and boffins; what do see when you see a circuit.

A circuit diagram highlights the functional positioning of components

A component location diagram highlights the spatial positioning of those components.

These are quite separate forms of information. You eventually need both.

With only a location diagram, you'll have a hard time figuring out what it does and how it does it.

With only a circuit diagram, you can work out which part you want to do something to, but can you find the little blighter?

The electrical systems in modern vehicles are quite complex. A main agent had one under warranty returned. It was probably the little black box of electronics that later did the duty of the old flasher unit. They had a circuit diagram, they had the expensive car. No layout data. Where was the <insert appropriately Germanic swear word here> thing? They spent days taking out the dash and looking, Every black plastic box was identified as something else. I got asked to help. Did I have something that could trace the wires to wherever it was without opening the looms?

Nope. I went into their showroom, borrowed the keys to the display one, turned on the indicators and tick, clunk, tick, clunk... ah, there it is. Hidden behind plastic trim to the right of the driver's foot! Amongst the door hinges.

Sometimes just finding the electronics can be a game.

Hiding it can be fun too. Or deadly.

With all the moving of a VHF Hallicrafters in the past few days, I remember reading 'The Battle of the Beams" The Germans were using VHF beams to guide bombers. Somehow we cottoned on and found them, but investigation of a downed bomber found nothing. Eavesdropping on the crew, now POWs got "They'll never find the receiver!"

It was hidden in plain view. Their beams were a higher powered version of the Lorenz landing aid. The aircraft had that receiver, but it had been made a lot more sensitive than necessary... a-ha! Gotcha!

It takes an impish mind to hide things well deliberately, but it's also easy to make things difficult by simple oversight and not thinking about the poor b'stard who has to come along later and work out his own way around it.

If you are in manufacturer's development group, and you don't do a good job of actively making things clear, YOU are the one all the problems gravitate to. That bit of circuitry you're so proud of... nobody thought of doing it that way before... no one's ever seen one like that! is the one that condemns you to keeping explaining it over and over again.

We've got design for this, design for that.... cost, manufacturability, test. Which blithering idiot left out understandability?

Anyway, Theoretical and spatial diagrams are both essential.

David
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Old 12th Sep 2020, 8:18 am   #64
wd40addict
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Default Re: Grey beards and boffins; what do see when you see a circuit.

Sometimes I've looked at a diagram and thought 'how can that work?' and assumed I'm missing something subtle. Down the line I then find my initial thought was right.

On starting a new job in the 90s I was presented with a multiplexer circuit designed by a predecessor (no longer with the company). A small batch were about to be built. It used FETs to switch 8 inputs down to one amplifier/filter chain. Like the Tascam circuit gate biasing was incomplete. When the first unit was built my initial thoughts were correct and it didn't work, a high value resistor to bias the gate fixed it.

I'm not sure how much this helps Andy, but a lot of it comes down to experience and familiarity with the 'blocks' you encounter.

Some musicians can look at sheet music and hear the music in their heads and I think we get the same with circuits. I still find it very difficult to read sheet music, let alone hear it in my head, no matter how hard I try.
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Old 13th Sep 2020, 11:17 am   #65
David Simpson
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Default Re: Grey beards and boffins; what do see when you see a circuit.

Andy, in his profile, says that he is "getting back into electronics" after quite a few years. I can emphasise with that, having made the same journey back in 2007. Take oscilloscopes for example - three "bread & butter" ones which I worked on back in the 60'/70's - Hartley 13A, Solartron CT436, HP180A. Ancient basic circuit diagram for the 13A, the CT436 was a lot more complicated, then the 180A - jolly complicated. The writing was on the wall I guess, for understanding the rapid advancement in technology. As a consequence, upon leaving the RAF in '75, I deliberately turned my back on Radio/Electronics/Avionics, & absorbed myself in a commercial diving career, plus house building & renovation, and a later career in electricity distribution.
Then along comes a retirement pastime in vintage radio/electronics many years later. A kind chap gave me a couple of u/s Telequipment D76 scopes - Jesus, I struggled with the circuitry & circuit diagrams. Several years later I acquired a heap of 1980's/90's college 'scopes - Gould, Wavetek, Hameg. I was completely flummoxed. Not only has the circuitry advanced amazingly, but so has the format of circuit diagrams.
So Andy, you're not alone in your quest to understand the complexity of modernish c/d's, as well as as old domestic radio's ones with their often lack of detail & working information.

Regards, David
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