Lead dress - Let's do the twist

[LPC78wino]

In the past, I was informed that I had over twisted the heaters on a 1992 build. Understandably so, as it was my first build and just did the best I could with instructions. Got crafty and used the trusty ole Black & Decker corded hand drill to twist the heater wires.
After the nice looking install, I had shown it to a very respected builder, and although he liked the effort said that I had created some sort of magnetic rod. I don't remember, but I had to redo it. Roughly three twists to each tube socket, like Marshall always does.

All I could find is a cool .gif showing what twisted wires do the the magnetic field - eliminating unwanted noise. Nothing about over twisting wires for this purpose.
So what did I do exactly over twisting the heaters and causing this magnetic disturbance in the signal? Is there a technical name or term for it? Always wanted to know or officially clear that up. Thanks

[pdf64]

The ‘magnetic rod’ thing seems a bit unusual to me. Maybe ask him to explain it to you again when you next meet up?

[LPC78wino]

It was long ago and not sure, using the wrong term, that is why I'm asking.
I vaguely remember something affecting and defeating the purpose of twisting too tight.
Probably not a magnetic rod, but that it's turned into more of a solid rod. Make sense?

Basically what the term is, or what it's called when two wires are twisted very tightly (e.g. using a power drill). It now has turned into some type of 'rod' and not as effective as hand twisted a few times?
Not sure if this helps visually.

[ChopSauce]

Is it just a fancy gif or the result of some simulation?

It's not that it's incredible, it's just that it doesn't make much sense.

Your advisor I wouldn't trust that much, given the informations you published here...

[pompeiisneaks]

I've used the drill chuck method to twist my wires in the past with no problems whatsoever. I don't get the 'magnetic' reference either. The ac going on in the wires is cancelled by the winding, because the direction of the interference now goes directly to the other wires opposite direction of interference, thus cancelling the noise. To create a magnet, you wind electric wire around a ferromagnetic center and send current through the wire. there's no 'center ferromagnetic material' here...

~Phil

[brewdude]

I’m curious, we’re you experiencing an issue that was solved by loosening the twist of the filament wires?

[LPC78wino]

To point out, my curiosity is in the heater wires only. Other wires such as choke wires didn't matter. It was the lead dress he was pointing out. I was asked if I'd ever seen Marshall twist wires like that, and obviously my answer was no.

I am looking for the term of two wires when tightly twisted together (in signal path).
Vaguely remember vintage Bell Telephone wire? or audiophile - tube receivers? Or RCA tubes?



Yes, the graph was a .gif. I just did a google .gif image search of noise cancellation examples.
My limited electrical background, but for lack of terms, I think I might have wanted to say electro-magnetic fields and not magnetic?
I apologize for this confusion as this is new to me.

I'll keep looking.

[sluckey]

Don't confuse twisted filament wires with twisted signal wires. Twisted signal wires usually applies to balanced signal lines. The twist is there to minimize ***OUTSIDE*** interference on the desired signal. Twisting filament wires is largely a cosmetic thing. I've seen very successful, well built amps with tightly twisted, moderately twisted, and absolutely no twisted filament strings. They all work very well. So don't put too much faith in the "properly twisted" internet sayers. Most are just micmics with little technical background.

[LPC78wino]

okay thanks. If something comes along that points to what tightly twisted or over twisted heater wires and their affect are called, I'll post it.

It's true though, that I've never ever seen heater wires like that done on any Marshall. Maybe that's a part of it, and guessing why he would have told me to redo my heaters on the Superbass build?
There was never an issue, just wanted to know what the terminology is.

[sluckey]

Ask the guy that told you to redo it. And post his answer here while it's fresh. I'm curious to hear his story.

[erwin_ve]

Overtwisted wire can damage the insulation, I cant think of any other refrences.

[ChopSauce]

I also saw broken wires from excessive twisting...

Nothing can defeat brutality, probably... still not much interference related.

[Phil_S]

Look at the Trainwreck photos. IIRC, it's a relaxed looping more than it is a twist. This was from someone who, I think we'd all agree, was a perfectionist. Lots of amps are built with a filament harness that was chucked in the drill. I've got an old Gibson with filament wires that just lay on the chassis floor, no twist at all. I agree, it probably matters a whole lot less than what some lead us to believe.

[pdf64]

Don't confuse twisted filament wires with twisted signal wires...

My understanding is that twisting the wires in balanced systems should be universally beneficial, whether the associated circuits are low level - high impedance which would otherwise be at risk of being contaminated by external field, or high level - low impedance which would otherwise generate an external field that might cause contamination.
ie receivers or transmitters or somewhere in between.
eg mic signal, heaters or LTP outputs respectively.

In balanced systems -

• twisting receiver wires helps to ensure any externally induced interference signal will be equal in both wires, and so be rejected due to being ‘common mode’.
  
  twisting transmitter wires helps to minimise any external fields created.

Various valve guitar amp implementations over the years have shown that the overall 3D routing of wiring within a chassis seems to be more significant than whether balanced wiring is twisted.
ie twisting balanced wires is more of a ‘best practice’ than an essential.
Merlin advises that for twisting (heater wiring) to be truly beneficial, it should be very tight http://www.valvewizard.co.uk/heater.html
I think the take away is that twisting balanced wiring almost certainly won’t do any harm and may be beneficial, though any untwisted balanced wiring is unlikely to cause a problem per se, provided that the rest of the lead dress / routing is done well.

[norburybrook]

from my limited experience I've come to the conclusion a lot of this is down to 'tradition' of the various amp makers and ranks along the difference between eyelets/turret board/tag strip etc.

Marshall amps historically have always had fairly loosely twisted heaters that lie flat on the chassis in comparison to fender/Dumble who fly them so it looks strange if you see flown on a Marshall and vise versa, same with a fender amp using turret boards

I know Amp Mike(modulus amps) on the forum here uses parallel untwisted wires in his amps to good effect, and Soldano has parallel spaced heater wires which look very cool (not sure if they're DC or not though)

Anyway, I think your friend was just being a victim to tradition here more than anything else.


M