Wire dressing guidance

[bristol]

I have been looking at a number of clones (Metro, Germino, Cieratone, etc.) and original JTM45s. They all seem to dress the wires differently. The new GPM45 head, for example, is dressed differently from the JTM45 kit instructions. In particular, the wiring from the output transformer to the power tubes and impedance selector as well as the AC wiring from the PT to the rectifier, switches, and fuse holders. Can anyone advise me in this area? I know some wires should be twisted (AC mostly I believe) others not. At the same time there is a trade off between wire length and twists, which naturally lengthen the wire. Some carry high voltage, some low. Some, low level signals and some high. Should low level signals be twisted with a ground that is nearby? Some wires should be kept as short as possible, others perhaps don't matter. Which wires can be left longer to enable neater wire routing and dressing? I have noticed that on some builds, all ac wiring from the power transformer to the heaters, and power switches, etc. are pretty much braided together (looks cool) So what is best?

Thanks

[thousandshirts]

That's a good question. At the risk of sounding obvious, though, I would suggest that you try to adhere to the photos in the MetroAmp JTM 45 Instruction manual. Some other JTM 45 makers will route their wires a bit differently, but at this point it is nothing to get obsessed with in terms of the visual appearance. What you need to ensure with your lead dress is a properly working (no hiss, hum, crackle, noise) amplifier.

By starting with the stock MetroAmp JTM 45 Instruction manual as your guide for wiring, you will not be steered wrong. You may personally find that the experience of building an amplifier will lead you to want to re-do certain bits of wiring, and that is fine; just unsolder, rewire, and solder once again. It's not like a special surgery you can only do once.

One thing I see in builds here a bit more than I might like is poorly twisted grid wires (coming from the phase inverter output, after the .1uf output coupling caps, on the side of the board nearest the potentiometers, and going to pin 5 of each KT66 socket). Keep those twisted up tight, from the board all the way to the output tubes, as far as you can (until they have to split apart to make it to their respective tube sockets, etc)

And don't obsess over going super tight with your twisting - you want it to stay put, and be quiet, yes. But you don't need to keep yourself awake late over it. Don't worry about "looking cool." Everybody does. I assure you, having your amplifier "look cool" on the inside is just as important as those people who "looked cool" in the high school yearbook photos, but now, years later, look like complete dorks. What you want is a properly functioning amp. Concentrate on that first. The instructions from MetroAmp will not steer you wrong.

Also, I don't think you should be concerned with the idea that twisting too tightly introduces 'overly long' lengths of wire into the circuit. Overly long lengths of single wires strewn about the chassis like a rats-nest, of course, is a bad thing, but a nicely tucked away twisted wire being 5" longer than one that is twisted not-so-tightly is a concern you can leave for another day.

In particular, the wiring from the output transformer to the power tubes

Twist 'em. These are on the "in" side of the OT. Don't twist the center tap (CT) of the OT with these two, though.

[and from the output transformer to the] impedance selector

Twist those, too. But these are from the "out" side of the OT, and twist them separately from those on the "in" side of the OT.

as well as the AC wiring from the PT to the rectifier, switches, and fuse holders.

At some points you'll only have a single AC wire, as it goes to and from a fuse or one side of a switch. That's fine. But if you can find a way to twist pairs of AC together, then twist again, like you did last...summer?

Some carry high voltage, some low. Some, low level signals and some high.

Again, follow the MetroAmp kit instructions. But -- just FYI -- Go to this page and read it: http://www.el34world.com/charts/currentflow.htm" onclick="window.open(this.href);return false;

The amp in the current flow diagram is a JMP 50 type amp, so there is no tube rectifier, and some of the component values are a bit different. However most of the the amp remains the same, and the same principles apply.

[bristol]

Thanks, I'll follow your advice.

[bristol]

Nice work on the JMP 50!

[bristol]

I meant on the 45/100.