Question about reading a schematic

[thornev]

This is not so much a Fisher related question but does apply since I've been working on restoring and modding my 500-C and I have great respect for the electronics knowledge that several people have who participate in this forum.

When reading a schematic and I see a component that is connected to other components via a dot and several lines proceeding away from that dot, if those lines lead to other components indirectly, such as through lines that lead to other components, can the original component be connected via any of those connected circuits as long as a circuit eventually leads to another component connected via those lines and dots? Or does that original component have to be directly connected to whichever component, and it can be several, is the closest to it?

For example, I have a schematic (attached, a simpler schematic just to make it easier to answer my question and is a radio on which I'm working to restore) and if you look at R6, it's closest connections are B+ (which comes from the + side of C11b), C15 and C9. Does it matter to which of those closest components I connect R6? If it matters, how does one decide to which component to attach R6? Or could I connect R6 to say pin 5 of tube 50L6GT since C9 is also connected to that pin?

Thanks for answering what probably is a novice question for several of you. I've tried looking online for a schematics course, but I've found nothing that answers this specific question. Thorne

 

[whoaru99]

An electrical schematic, generally, is just to show how the bits are electrically tied together, not to show the physical layout/assembly.

Unfortunately, there is no one answer to your question. In some cases physical layout relative to electrical interconnection isn't terribly important/critical, but in some cases it is.

 

[thornev]

Thanks, Who. Can you give me examples of when it matters and when it doesn't so I can understand a little better? Maybe use the schematic I posted to illustrate?

 

[Beemerdoc]

Maybe this will help:
I think of the current in the above signal kind of like water. It starts at the water plant (B+ in this example) and it goes into a pressure regulator (R6) and then on to feed several "houses"
(C9, C15, and pin 5 of tube 50L6GT). I think that the important thing is that all these "houses" are fed after the pressure regulator so as to not blow the pipes out of the respective houses.
In actual service, there may be a big boulder in the way to some of the houses, so they have to take the pipeline around it to accomplish this.

I hope this gives you a different approach on the issue at hand.

 

[dr*audio]

Lengths of wire can act like an antenna and pick up noise that can then be amplified. Therefore, components that are shown on the schematic located near and connected to each other should usually be located near each other in any piece of hardware, unless the schematic is poorly drawn or the layout was poorly done. I have seen both. I think I can say in all cases, if there is a pin of a tube or transistor shown on the schematic to be connected either directly to ground or through a resistor or cap, that connection should be as close as possible to the tube or transistor.

 

[thornev]

Thanks Beemer. I get it for resistors. For capacitors, after the water pressure is reduced by R6, do C9 and C15 reduce the amount of water the houses get via the DIAMETER of the water pipe (which in a way also reduces the AMOUNT of water that gets through but via a different method)?

 

[Pio1980]

Dashed lines between component symbols indicate mechanical linkage. Dashed lines around components or sections may indicate a modular section or shielding/ screening.

 

[Beemerdoc]

A capacitor is a storage device. I see them as water towers in our example to ensure enough water available to all users at any time.

Mind you, I am not an electronic engineer nor a builder/repair person in this audio world. My electronic experience is gained from years of automotive repair and trying to actually fix things instead of just replacement of parts. Though, when you think about it, isn't repairing an amp very similar? Track down the offending component and put a new one in.

Just trying to help with my limited expertise.

 

[thornev]

Thanks Pio. What exactly do you mean by "mechanical linkage"?

Are the dashed lines from L1 to L2 an example in my post #1 schematic? If so, what exactly is mechanically connected?

Or maybe the diashed box around "MI" is an example? If so, does that mean there are 4 leads emanating from "MI"?

 

[Pio1980]

Thanks Pio. What exactly do you mean by "mechanical linkage"?

Are the dashed lines from L1 to L2 an example in my post #1 schematic? If so, what exactly is mechanically connected?

Or maybe the diashed box around "MI" is an example? If so, does that mean there are 4 leads emanating from "MI"?

The two coils are permeability tuning elements that are mechanically linked by the tuning mechanism, M1 is the clock module unit.

 

[thornev]

Yeah, Beemer. There's a HUGE difference between tracking down a part and immediately replacing it, and verifying when you replace a part, that, should you forget where it was connected, using the schematic to locate the physical connections in the chassis which requires at least a minimal understanding of how components work together and what they do for the device. The latter is the part about which I'm having trouble finding classes and online documentation.

One thing I've been doing is taking lots of pictures of the chassis from different angles BEFORE I remove any parts (or I do it in stages for large units like receivers), so that I can go back and have an illustrated reference.

 

[whoaru99]

Thanks, Who. Can you give me examples of when it matters and when it doesn't so I can understand a little better? Maybe use the schematic I posted to illustrate?

A couple generic examples that come to mind would be resistors.

In once case, a power supply dropper, in my opinion isn't exceptionally critical where it is physically located as long as it is electrically in the right place. Something like that can run hot in some cases so physical consideration may carry greater weighting than purely the electrical placement.

On the other hand, something like a grid stopper resistor may be shown electrically close (or not so close to a tube) but typically should be mounted as close as possible to the tube. The body of the resistor more or less tight to the terminal of the tube socket, if you will.

 

[dr*audio]

A capacitor is a storage device. I see them as water towers in our example to ensure enough water available to all users at any time.

Mind you, I am not an electronic engineer nor a builder/repair person in this audio world. My electronic experience is gained from years of automotive repair and trying to actually fix things instead of just replacement of parts. Though, when you think about it, isn't repairing an amp very similar? Track down the offending component and put a new one in.

Just trying to help with my limited expertise.

That only applies to power supply filter caps. Otherwise it's an inaccurate and misleading description of what a cap does. Capacitors pass AC current and will not pass DC current. The current has to be changing or it won't pass. In the signal path, the cap is used to block DC voltage and only pass AC (audio signals in this case.) In the power supply, the caps filter out the AC ripple (60 Hz) by passing it to ground. Since they don't pass DC, they "store" it.
If you want to learn about electronics, a great book to read is "The Art Of Electronics" by Horowitz. It is written in easy to understand language. You don't need to know anything other than algebra. You can download it for free online:
https://archive.org/details/TheArtOfElectronics-2ndEdition

 

[audmod01]

In the case of radio/tuner/receivers, the connections of components in the RF and IF circuits in particular can be quite touchy. The higher the operating frequency of the circuit, the more important lead length and placement of parts becomes. For instance, a bypass capacitor for an IF transformer on the B+ supply side of a plate winding needs to be close to the IF transformer, not located several inches away or at the other end of the chassis. The longer a wire is the more it tends to act like an inductor or coil at higher frequencies.

Another area of concern deals with tube heater wiring versus audio circuits that can induce hum into audio. Lead dress of wires and components can become a significant contributor to hum contribution or the lack thereof.

Joe

 

[thornev]

Thanks, Doc. Download complete. This will be the 7th book from which I'm trying to learn. I am excellent at math.

I want it to be explained in simple language WHY one needs a resistor followed by a capacitor and HOW do the different values affect a circuit? And if I want to remove hum from my receiver, how do I go about finding it so I can add or remove the appropriate components. Stuff like that. I've have more books than I need that explains Ohm's Law. I really appreciate all the help everyone on this forum gives. Your explanation of capacitors in post 13 is perfect for me. Very helpful.

 

[thornev]

Thanks, Joe. You may have just given me a clue as to why I'm getting some low level hum in my 500-C. I did not use insulated wiring when I installed the IBAM and there's close to a foot of that wiring.

 

[Dave451]

Thorne,
I'm learning much as you are--trying to learn more theory at the same time as coming to grips with the more practical questions of electronics, such as in your first post above. Ohm's law is very important, but it will only get you so far. Something that might be more to the point for your situation is a book like Morgan Jones' "Valve Amplifiers."

He does start with very basic electronics (where you must start), but gets into what the components do and why it's important. He then builds on this progressively through the book with some very nice descriptions of the building blocks of tube circuitry (including what the individual resistors, capacitors, etc, actually do), starting with a simple triode tube amplifier circuit (12AX7/ECC83). He helps you understand the basics of tube design, like the load line and operating point, and builds on up to complete practical amplifier circuits. He also throws in some nice chapters on good construction practice, including lead dress, grounding ("earthing" in the book, as he is a Brit, as the title might hint as well), layout, etc. I have the second edition, bought used, and I think it's now up through the fourth. Something to consider and it doesn't sound like the math in it would hold you back.
Dave

 

[thornev]

Thanks, Dave. I have Dave Hunter's "Guitar Amp Handbook" which sounds like the same thing as "Valve Amps". And it is helpful explaining the parts of the amp and how they interconnect. Best book yet for me. I've started drAudio's recommended download book too which has some good info around a lot of complex math. I went all the way to Calc 2 in math so no worries there. I never thought I'd ever use Diff EQ though. Thorne