Internal Wiring

[Jack Sparrow]

I'm working on my shopping list for a 5E7 build and I'm trying to decide what kinds and colors of wire I need to order.

Is there any "standard" color scheme for the internal wiring of a tweed amp? Fender mentions the color of a few of the wires on their layouts. As best I can tell from the pictures I've been studying, it looks like yellow is used for most connections. Is that pretty much how you've done it or is it better to use certain colors for certain connections for future trouble-shooting?

Most descriptions recommend running the heater wires elevated above the tube sockets but some say they push the twisted pair into the corner of the chassis next to the sockets. Is there anything to beware of either way?

I've read recommendations of using shielded cable to the input jacks, the V1 tube grids, the treble control, and even the power tube grids. Necessary? Where do you ground the shield if you use shielded cable? Can you use two conductor shielded cable to two input jacks or is it best to use single cables to each jack?

Thanks for your help.

[Chuck H]

About the only "standards" I stick to is black for grounds and red for HV. Other than that I simply try to coordinate circuits in color so that it's easier to trace the circuit (and harder to make a mistake) in case I ever need to open the amp up again. That is, all the cathodes will be one color. all the grid leads will be another, etc. I don't even try to remain consistent with which colors I use for which circuits. I just sort of wing it based on what I have in stock and how much wire I'll need. But I build mostly one off custom amps. I do stay consistent whenever I build an amp to order. That "model" will always have the same color codes. Many old Fenders were wired stock with one color for the assembly. With the only differing colors being those leads that are not cut from a spool. Like PT and OT leads. So I guess it's up to you if you want to color code the circuits.

[Enzo]

First off, you are building one amp for you, so it doesn't matter if Fender did it different. Fender had different needs than you have too. Look in Marshall amps, and you will find consistent use of blue, yellow, and green wires to the elements of the triode tubes. That might be helpful in keeping your leads figured out. But if you want to use pink, purple, and orange, go ahead. In the case of a Fender eyelet board, even if they had a color standard for the wires over to the sockets, there would not likely be much of a standard for ther wire running from eyelet 24 over to eyelet 56. Or whatever. SO yellow is as good as anything.

There were standards in the old days. At least in the USA. green for 6v heaters, yellow for 5v heaters, red for high voltage, blue for bias tap, black for primary, center taps would be of similar color with stripe added, those all on power transformers. As CHuck said, black for ground - or more properly common - is good, and red for high voltage. Your high voltage or "B+" might be red, but there are different levels of it, so if you want you could decide red for the main B+ supply, then orange for the screen node voltage, then whatever for lower levels. There was also a standard for output transformers, red for primary CT then blue and brown for the plate leads. Ultralinear taps would be blue and brown again but with striped added. And the secondaries had colors too.

It would be great to have 20 colors and colors/stripes, but unless you are going to be building as an ongoing thing, you will pay a lot for excess wire you won;t use, so it might make more sense to get only a couple colors and take steps to keep track of the wires during construction. For example, if you have all yellow wires, you can use a sharpie and make little marks on the insulation near the end. Say, 1 mark for plate, two marks for grids and three marks for cathodes. Or two marks side by side versus two marks spaced apart. Make something up.

Rermember in grade school they had little round circles of glue-on paper to reinforce the holes on your three ring binder pages? "Hole protectors" or some such? A friend of mine used those. He glued one around the end of every ground wire, and he'd say "the round is ground" to remember. Even little tabs of masking tape with numbers written on them, and you tear them away after the build. There are many ways to keep wires straight. Oh, and that guy grew up to be an electrical engineer, working on space exploration satellites. I fix guitar amps. Oh well.

Color systems are there to serve YOU, not the other way around.

[Steve Conner]

This is my standard wire shopping list:

Thick green (European 32/0.2 size)
Thick red
Thick black
Thick yellow

Thin red (European 7/0.2 size)
Thin green
Thin blue
Thin black

RG174 miniature coax

Thick uninsulated copper wire (I usually salvage it from surplus house wiring)

To tell wires of the same colour apart, I use Enzo's trick of dots from a sharpie marker, or if I'm feeling ghetto I'll tie a knot in the positive one.

[Enzo]

OH wow, never occurred to me others did that. Forever, if I have a couple wires emerging from something, I knotted the positive one.


Not too tight a knot, though, it pinches off the electrons.

[Chuck H]

OH wow, never occurred to me others did that. Forever, if I have a couple wires emerging from something, I knotted the positive one.


Not too tight a knot, though, it pinches off the electrons.

Yes it does. But that's the inductance. Your adding mojo by introducing hand wired elements that you can't buy. nd you can adjust the effect by loostening or tightening the knot. Rarely will you ever need two knots. That would be silly.

[Jack Sparrow]

Yes it does. But that's the inductance. Your adding mojo by introducing hand wired elements that you can't buy. nd you can adjust the effect by loostening or tightening the knot. Rarely will you ever need two knots. That would be silly.

Does it have any effect on volume? I'd be afraid that if I knotted the output transformer wires, there would be some risk of bursting.


Seriously, you all have good points. I really like what this guy's done. (He's one who tucked the heater wires into the corner.) But I wanted to do it "the right way" for anyone who ever sees it. OTOH, it's not like I'd be trying to trace one pair of wires through a bundle of fifty. It does look like Fender only mentions the colors where multiple wires are routed through a single hole to keep them straight.

So what about the shielded wire? Where to use it and where to ground it?

I must say that I'm learning more than I ever realized I didn't know. It's been an interesting education so far.

Thanks for that.


Here's something to think about. Why is "1" the lowest setting on some amps? Isn't that like a car speedometer that starts at 10 mph?

[Chuck H]

Ususally a shielded lead is coming from a pot. And usually that pot has one lug grounded. Usually the shield is grounded at the pots grounded lug. And if done properly the other end is trimmed and shrink tubed.

That's a neat effect with the blue on blue. But it sort of forces component choice. Neat is good too. But should really be second to stability in any layout considerations.

On most amps 0 is the lowerst number. So if you take the tweed panel and subtract the "1", as you necissarily do, they still go to 11. Nigel would approve.

[Jack Sparrow]

Yeah, the blue is cool, but I was referring to his wire dressing and bundling techniques.

[KFTG]

Jack Sparrow, when choosing wire, I would go with a solid wire. Much more easy to work with. Colors,,, black is ground... yellow is signal... heaters are white...red is b+. The most important thing to remember is lead dress. Keep the signal wires as short as possible, and when intersecting with b+, make sure you have a true intersection, as is a street intersection. If you run b+ along side a signal wire, you will get hum or noise. Another thing that comes to mind is make sure your power supply grounds are grounded at the power transformer, and you front end is grounded to the input jack. Very important. Keep your front end tube as far away as possible from the power transformer. Hope that helps you out.

[Chuck H]

Colors,,, black is ground... yellow is signal... heaters are white...red is b+.

Who said? Most guitar amp filament leads are green. Marshall uses yellow for cathodes. Where does this standard come from?

If you run b+ along side a signal wire, you will get hum or noise.

Actually, that's usually not an issue. But it can be so no foul. Marshall use to tack the plate and grid leads for the input triode together on the chassis with some mystery white goo. I assume the purpose was to glean a little capacitance, and therefor increase HF stability, from the circuit. Filament leads are a bigger danger. Keep those away from signal leads.

Another thing that comes to mind is make sure your power supply grounds are grounded at the power transformer,

Actually... Power supply grounds should be grounded as they happen in the circuit. That is, the power amp filters should be grounded with the power amp, the preamp filters should be grounded with the preamp. At least that's the ideal way to do it. I have grounded all my filters together at the power supply without issues too though. On individual leads. Never daisy chained.