The gauge printed on a spool of hookup wire, translated into what it can carry and where it actually belongs inside a chassis — from the heavy mains lead down to a grid lead barely thicker than a hair.
AWG numbers run backwards from diameter — the smaller the number, the thicker the wire — on a scale where every 3-gauge step roughly doubles the cross-sectional area (and every 6-gauge step doubles the diameter). It is a geometric ladder, the same shape as the dB scale on the units & notation guide.
| AWG | Diameter | Chassis-wiring ampacity | Typical use in an amp |
|---|---|---|---|
| 14 AWG | 1.63 mm / 0.064 in | 32 A | Mains lead, chassis safety earth |
| 16 AWG | 1.29 mm / 0.051 in | 22 A | Power-transformer primary, HT bus to first filter cap |
| 18 AWG | 1.02 mm / 0.040 in | 16 A | Heater wiring (18–20 AWG), B+ distribution |
| 20 AWG | 0.81 mm / 0.032 in | 11 A | Heater wiring (18–20 AWG), speaker leads |
| 22 AWG | 0.65 mm / 0.025 in | 7 A | Signal wiring (22–24 AWG), pots & switches |
| 24 AWG | 0.51 mm / 0.020 in | 3.5 A | Signal wiring (22–24 AWG), tight tag-strip runs |
Two ranges cover most of the wire in a point-to-point chassis. Heater wiring runs 18–20 AWG — a 6.3 V winding is low-voltage but not low-current, and a twisted, dressed pair keeps its hum off nearby grids. Everything else — grid returns, pot and switch wiring, tone-stack legs — is signal wiring at 22–24 AWG, thin enough to route through a crowded eyelet board without stiffening the layout. The gauges below that pair are reserved for the mains lead and the high-voltage bus, where fault current is the concern, not signal.
"Chassis wiring" ampacity assumes one insulated conductor in free air, not bundled with others — a conservative bench rule of thumb, not a building code. Point-to-point amp wiring almost never approaches these ceilings; what actually decides a gauge is the insulation's voltage rating, whether it fits the lug or eyelet it is soldered to, and whether it survives years of heat next to a power tube — not raw current capacity. See the Ohm's law calculator for the I·V·R·P sums behind any of these figures, and the transformer reference for how the power transformer's own colour-coded leads carry the heavier currents on this table.
Before PVC and silicone hookup wire took over, tube-era chassis were wired in a braided cotton or rayon sleeve over tinned stranded copper, most commonly in the 20–22 AWG range — right in the heater and signal gauges above.
The braid is wound loosely enough to slide — "push back" — off the last half-inch of conductor, so the wire needed no stripper: a fingernail and a twist bared tinned strands ready for a turret lug or an eyelet board. The wax or lacquer impregnating the braid gave it a working voltage rating and a little resistance to the heat radiating off a nearby power tube, in place of a plastic jacket.
It is still made and sold today, mostly for the reason it was used originally — builders reproducing or restoring an amp from this era wire it point-to-point the way the factory did, in the same 20–22 AWG range, often colour-matched the way the power-transformer leads are.
Diameters and the chassis-wiring ampacity above follow the American Wire Gauge standard and its published load chart — Wikipedia, "American wire gauge" and the PowerStream AWG wire size chart, itself drawn from the Handbook of Electronic Tables and Formulas for American Wire Gauge. Treat the ampacity column as a bench rule of thumb, not a code reference — anything feeding mains current should follow the National Electrical Code and a qualified electrician.