Going from schematic to physical layout

[grindliner]

Can anyone point me in the right direction, or to a book that addresses coming up with a physical layout from a schematic.

I've just read the Torres, Weber, and Funk books, but unless my brain is on overload (I've read em all over the past week), none of the books explain how to go about it. I know one of them (I think Torres) Mentions Tube spacing.

[Chris G]

While I'm in no way an authority on the subject I have built a bunch of amps from scratch.

First thing to do would be to look at as many amp guts as you can. A real good place to start would be any Fender amp ever made. If you were referring to Gerald Weber's first book, It is loaded with schematics and Parts placement diagrams. You will start to see very quickly that most amps share a physical layout. as far as measurements and spacing goes if you search this site I'm sure the early trainwreck files will have chassis dimensions on where to put sockets,trannies,switches,etc. Hope this helps.
Thanks
Chris

[GibGa]

Its easy really. From schematic to layout you need only visualized the actual parts going to the connection points and sketch it out. Start with a simple schematic for practice 5F1 champ or such.

A resistor and Cap are shown at pin3 in the schematic notation. Draw a realistic representation of the board and tube sockets and pins and location on the board to scale full size, attach the res/cap to pin 3, then the other res/cap lead end to the board eyelet. And so forth and so forth. Even reading a book you'll eventually have to cross into this process, so forget the book search and sit down with paper and draw it out. After a few minutes it's a cinch really. Then move to bigger complex layouts. No big deal. Same with a cad software set up if you prefer, but I like the old paper and pencil and the actual drawing process myself.

[Structo]

I agree that it is probably best to copy a well known and successful amp layout.

Doing so from scratch or an original idea is a big jump from a schematic.

By copying a known working layout, you will avoid bad habits that can cause cross talk between components and oscillations.

You need to observe the physical spacing between components and the way the lead dress is in a chassis.
Fender made a lot of mistakes along the way but many feel their amps are among the best.

That's why building a kit where this homework has been done for you is an excellent way to get into building.
Then you can use that experience and the amp you built as a spring board to your own designs.

[mcrracer]

Get a big honking eraser! If you're like me a lot of mistakes will be made early on until you get the hang of it. After awhile you will see certain circuits show up over and over so you can quickly draw them in. I draw most of my own layouts these days and / or modify existing layout to fit my needs.

[GibGa]

Yes to the Erasers! Very necessary. And colored pencils for wiring is nice if you do all hand drawing.

[grindliner]

Right now I'm working on a 1960 Airline 9002, which is very similar to a Champ circuit, but the tubes are a 6v6GT, 6X5GT rectifier, and a 6AU6 preamp. Problem is that I cannot find any info on this amp, but found a schematic for an Airline 9012 which appears to be the same with the exception of 2 resistors. odd thing is that one of them is bridging 2 pins on the preamp tube

While some of it makes sense, other parts do not.

I'm working on troubleshooting it at the moment, but for $30 who can complain.

[grindliner]

not only do I have lots of erasers, I even have a motorized eraser from all the f*cking drafting classes I had to take while serving my apprenticeship.

[tubeswell]

There are some principles that are useful (that I have found out in some cases by reading, or in other cases by trial and error), such as:

Keep signal wires as far away as practicable from high current AC wires, and where it is necessary cross them, only do so at right angles to each other (not alongside each other)

Try and economise on distances between subsequent components (keep component leads shorter rather than longer etc

Keep high power parts of the amp away from low power parts of the amp.

Keep transformers as far away as practicable from input sockets/cables. Have your first stage as close to the input sockets as possible. Have your PI as close to the power tubes as possible

Keep AC pairs twisted together (so that the EMF surrounding each respective wire is cancelled out by the other wire's EMF)

Keep AC wires close to the chassis (The chassis potential helps 'eat up' stray EMF)

Don't have high voltage eyelets/turrets close to low voltage ones (or signal ones) on the board (in order to minimise the opportunity for 'leaky board' syndrome)

Shield sensitive input cables up to the grid of the first stage (with the shield grounded at one end only), and even shield other signal cables from pot wipers to various grids, and even from the PI output coupling caps to the power tube grids if necessary.

Don't have lots of wires cross crossing each other in close proximity.

Follow a good grounding scheme that minimise the amount/potential of localised rises in ground potential, and minimise the amount of chassis ground return points. But ground your LFO grounds away from other grounds.

(Sounds like a lot of "Don'ts" I know )

[paulster]

One I'll add is try to position the board such that you minimise lateral wiring to the front panel controls as you've got the opportunity to induce phase-shifted signals into other parts of the amp, and once you've got your board position decided, try to place the preamp tube sockets so that they line up with the relevant components on the board that will be connected to them.

Less crosstalk means less chance of parasitic oscillations or other nasties that may require suppressing and more chance of the true tone to shine through,