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Schematic To Spaghetti And Back

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Schematic To Spaghetti And Back Empty Schematic To Spaghetti And Back

Post by Where did I put that... on Tue Jun 17, 2008 4:45 pm

Does anyone know of a book or website that can teach someone how to be able to look at the spaghetti under a radio and learn how it matches up with the schematic?

Sometimes my college electronics "education" from the early 1970s gets a little fuzzy, man, and all the pretty wires don't do anything for me except make the world more beautiful, man. Far Out!
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Schematic To Spaghetti And Back Empty Re: Schematic To Spaghetti And Back

Post by Resistance is Futile on Wed Jun 18, 2008 3:22 am

Thee spogetty:

Wire that is under the chassis is never as it appears on a schematic.
It may show a ground at one point and be somewhere,or, nowhere near the connection shown. Always try to find identified tie-points such as a tube pin number, as a starting point, Identify each pin number that has a passive component tied to the pin and identify what value it is. (resistor or cap) or active such as variable cap, transformer, IF can etc. When you have the wire you could wrap a piece of scotch tape around the wire by marking it with a number- letter combination. When you find a wire in the schematic that co-insides with the actual wire on the radio.

You could then number the schematic wire with the same number.
Using the schematic you can mark the sides of the schematic with grid marks, (such as 1,2,3,4,5 etc. across the top, then down the side with the letters a, b, c,) this will become your locator's map.


On the top side of the chassis use a pencil to write the tube # . Tube pin numbers are identified from the key from the clockwise movement. you can identify the RF variable cap as it has larger movable plates, the smaller ones are oscillator, You can also make a block diagram of each stage for easier identification when you need to for future reference.

Hope this helps, as it can be a nightmare unless your patient and persistent. And of course a tube manual will be of value in doing this.
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Post by Where did I put that... on Wed Jun 18, 2008 4:12 pm

That's a good idea. I know where I can get some wire labels with numbers in different colors, too.

Thank you!

How is Trillian?
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Schematic To Spaghetti And Back Empty Re: Schematic To Spaghetti And Back

Post by exray on Sat Jun 21, 2008 4:40 am

Where did I put that... wrote:Does anyone know of a book or website that can teach someone how to be able to look at the spaghetti under a radio and learn how it matches up with the schematic?

Sometimes my college electronics "education" from the early 1970s gets a little fuzzy, man, and all the pretty wires don't do anything for me except make the world more beautiful, man. Far Out!

Short answer is 'no'. A schematic is like a 2-dimensional road map. It shows all the connecting roads but doesn't tell you if there's a big tree along the way or if your are on a hill or in a valley. Schematic won't tell you thats the faded green wire running along the back of the chassis or the big old capacitor than spans a few inches across the chassis jumping over other parts of the circuit. Thats why there's nothing to teach.

The way to make it work, and a highliter can become your best friend, is just like Mr. Resistance says...find the identifiable starting points like tube pins and work from there. Terminal strips and such never have any numbering so the only really dependable constants are the tube sockets.

Ya just gotta do like the rest of us...trace it out. You may find three common points on the chassis for components that are scattered all over the schematic page and vice versa.

The best exercise imaginable is to take a radio and draw YOUR OWN schematic from its wiring and compare your results with a published schematic. It doesn't take but 2 or 3 attempts to observe how the draftsmen make all that spaghetti into a readable electronic drawing.
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Schematic To Spaghetti And Back Empty Re: Schematic To Spaghetti And Back

Post by Fisherdude on Tue Nov 11, 2008 12:33 pm

Just found this old thread, and thought I'd toss in a suggestion just in case the op is still here...

As you start to try to trace the wiring under the chassis, as has been mentioned you just need to find a logical starting point and dive in. Start from a fuse, or an input jack, and just dive in.

There is one particular thing that can cause a lot of confusion if you're working with vacuum tube gear, and that's the common practice of using unused tube pins as tie points. For example, a tube might have 9 pins, but there aren't 9 internal connections from inside the tube, so several of the pins aren't connected to anything. So, the designer of the radio frequently used that unused pin on the bottom of the socket as a convenient place to solder connections to other components that have nothing to do with that tube.

So, you see a bunch of wires soldered to pin 7 of a tube, but the schematic shows nothing "connected" to pin 7. In fact, the schematic doesn't even show a pin 7 for that tube. Try to follow those components "backwards" to something else you can identify, and you should be able to puzzle it out.

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