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Wire choice
#1
Hi Guys

When wiring a guitar amp, we have many choices about the wire, so how do we make sure we get the right stuff?

Wire has a gauge or thickness, denoted by a number: the smaller the number the fatter the wire. Gauge ONLY determines current capacity, and vice versa.

Insulation type can be cloth, PVC or Teflon, although there are some other poly names to confuse us - haha. Generally, PVC-insulated wire is the norm. Teflon is thinner and requires special wire strippers, so it can be expensive overall. Cloth is purely aesthetic and usually has a plastic inner layer to provide the actual insulation. Vintage restorationists prefer cloth-covered wire to maintain a vintage look, but the down-side is that most cloth wire is solid.

The insulation type determines the voltage capability of the wire. The cheapest wire will be rated at 300V, and 600V and 1kV ratings are available. In general, the 300V wire is good enough for most assemblies since the ratings are actually AC volts, so "300V" means 420V peak or DC. We are not concerned with the heating equivalnce between RMS-AC and DC; rather, the maximum voltage withstand capability.

Stranded-core wire is made up of many thin strands wound together forming a flexible overall wire. Solid-core wire is just that: one solid strand of wire. It is easily bent and holds its shape, which is why some amp builders prefer it. However, this same characteristic can make it more microphonic, too. We generally recommend stranded wire for all applications other than for buss wire on hand-wired cards.

TUT3 Chapter 3 discusses wire selection and wiring practice in detail.

Have fun
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#2
TUT3 is the amp wiring bible!!
It was a bit tricky following the wiring method in my Marshall but in the end I got it done and it is SUPER QUIET Smile
makes you wonder why they didn't do this at the factory?
Thanks Mr O'Connor
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#3
I just purchased a 100' spool of alpha RG-174 shielded wire. For regular hookup wire, I like the 20 and 22 AWG stranded wire available from TubeDepot.
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#4
Hi Guys

RG-174 uses copper-clad steel inner conductor with tinned-copper braid shield. The shield is okay but the inner conductor adds distortion for audio signals. This may not be a concern in a guitar amp but for your hifi you will want to use all-copper.

Since this coax is designed for use at radio frequencies, the distortion is not present at RF as RF travels on the wire surface (skin effect). Low-frequency audio is a "bulk" signal travelling equally within the cross-section of the conductor.

It's hard to beat the low-capacitance.
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#5
What would you suggest as a substitute for RG-174, Kevin?
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#6
Hi Guys

That would depend on which of the RG-174 parameters are the most important to you and what you were using it for? Obviously, we are interested in using for audio, but is for inside or outside of a chassis? You can use the same coax for both but you might have to be more careful about not stepping on foil shield more than braid, for example.

Inside the chassis you try to use thinner diameter coax and 2-conductor cable especially if there will be a lot of wiring. Remember that all the currents in a tube amp are low, especially signals in the preamp where you are likely to want coax, so the inner conductor gauge can be very small. Voltages are low, too, so the insulation layer can be thin, which should lead to lower capacitance.

Note that it is a mistake to shield all three connections to a triode as this adds significant capacitance and kills the frequency response of the circuit. Running the grid only through coax is okay.

Braid provides better magnetic shielding than foil-plus-drain-wire. Foil provides complete electrostatic shielding. So you decide which is more relevant in the chassis or for a given signal run.

Since manufacturers change their product line every now and then, and because availability of certain wire is inconsistent or changes, too, it is best to use the search functions at Mouser or Digikey to see what is available with the specific priority of parameters you might have, and then with altered priorities. That will give you actual part numbers and brands that you can use to check availability from other suppliers.
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#7
I'm quite fond of this stuff
Aircraft Spruce is the supplier

https://www.aircraftspruce.com/catalog/e...ldwire.php (usa)

https://www.aircraftspruce.ca/catalog/el...ldwire.php (canada)



It works wonderfully for input signals and long runs under boards to control pots.
Tinned inner and shield. Tefzel sheath and mill spec for aircraft instrumentation and signals. It is Very thin. The 20ga shielded, is slightly thinner than regular non shielded PVC jacket 600v 18ga stranded I have. Unlike most chunky coax I've seen.

Also they have wonderful 18ga, 20ga and 22ga non shielded wire in many colours. All 600v. Reasonably priced and shipping wasn't terribly expensive for the amounts I've ordered.

Cheaper than the Ebay guy that sells 10ft chunks too!


I've never needed special types of wire strippers but I've got a nice set that has many gauge options as well as an old fashioned style that you can manually adjust to any size. Although I don't normally use that pair.
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#8
Thanks for links! That looks like it's perfect for amps.
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#9
Hi Guys

Just for reference, in the Q&A section for the wire Jollyjoe bought, there is size given for #20 shielded:

"What is the diameter of 20 awg shielded wire? 
The diameter of shielded 20ga white wire M27500-20TG1T14 part # 11-14420 is 2mm."

That's pretty nice for inside equipment.

What is Tefzel? A brand name of Dupont, just like Teflon, for an insulation often referred to as EFTE - Teflon is often referred to as PTFE. There are many articles online that discuss the properties of these insulations, such as this one:
https://www.lectromec.com/an-overview-of...-and-etfe/

and this chart from NASA:
https://nepp.nasa.gov/npsl/Wire/insulation_guide.htm

The chart lists Teflon as being "more flexible" but this is relative to some of the other MIL-spec wire NOT to common PVC-insulated wire.

Have fun
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#10
Hi Guys

At the other end of the spectrum you will find wire like this, from an Aliepxpress vendor:
https://www.aliexpress.com/item/28AWG-25...2e0ejmod6b

They sell 1-meter pieces but will sell continuous lengths if you request it and are buying much more.

The OD is not excessive. The insulation is just PVC so you have to be careful not to overheat it or touch it with the soldering iron. I used wire like this from suppliers close to where we used to live and it is fine when you deal with it correctly - not too bulky, low priced, convenient to handle. In short lengths inside an amp the unknown capacitance is not a problem and the spiral shield has some benefits over a foil shield with drain wire, although there is a trade-off in both directions of that comparison.

On their page, you can change the quantity and see the total price of wire + postage go up incrementally. The price goes down from 1m to 4m then jumps back up nearly to the 1m price at 5m. From 6m on it drops slowly all the way to 100m. So, you should check these things before you order a medium quantity. You do not get down to the 4m price until 16m.

Have fun
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#11
For those of you in the USA McMaster-Carr is an excellent source for rolls of PVC covered wire. It's not too expensive and comes in loads of colors. They are also a good source for garolite for circuit boards.

https://www.mcmaster.com/standard-electrical-wire
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