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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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