The iron in a tube amp does three jobs — step the mains up for the plates, step it down for the heaters, and match the output tubes to the speaker. This is the lead-colour code for the power transformer, every transformer and choke in the archive, and the one sum behind an output transformer's ratio.
A tube-amp power transformer brings its windings out as loose, colour-coded leads. On the tweed-era Fender drawings the code is consistent: hover a winding below to read its leads, or work from the chart. The centre-tap leads carry a second colour as a tracer stripe.
Hover, tap, or focus a winding to name its leads.
| Lead | Winding | Carries | |
|---|---|---|---|
| Black + Black | ×2 | Primary | Mains input, ~120 V AC — switched through the fuse and power switch |
| Red + Red | ×2 | High-voltage secondary | Plate supply to the rectifier — the ends of the HT winding (325-0-325 V AC on both drawings) |
| Red / yellow | ×1 | HT centre tap | Midpoint of the HT winding — the B+ return, to the first filter / ground |
| Yellow + Yellow | ×2 | Rectifier filament | 5 V for a directly-heated tube rectifier — 5Y3GT, 5U4G, GZ34 |
| Green + Green | ×2 | Heater secondary | 6.3 V for the preamp and power-tube heaters |
| Green / yellow | ×1 | Heater centre tap | Midpoint of the 6.3 V winding — hum reference, grounded or elevated (present on the 5F6-A, not the 5E3) |
Lead colours read directly from the published Fender layout drawings: the "Deluxe" 5E3 (F-EE) and the "Bassman" 5F6-A (I-EG), both archived at EL34World. The diagram is redrawn here, never traced from the source documents. For the gauge those leads are actually wound from, and the cloth-covered hookup wire strung between them, see the wire gauge reference.
Every transformer and choke listed in an amp's parts list, generated straight from the archive at build time — 21 transformers and 6 chokes across 10 circuits. Where a drawing prints only a Fender part number, that number is what appears here; where it prints an impedance or a winding voltage, that does.
| Part | Spec | In circuit | Role |
|---|---|---|---|
| Power transformer | HT · 6.3 V · 5 V | 5E1 Tweed Champ-style | HT secondary (voltage not marked; +320 V reservoir implies ≈325-0-325) + heater and rectifier windings |
| Power transformer | 325-0-325 V · 6.3 V · 5 V | 5E3 Tweed Deluxe-style | HT + heaters + rectifier filament |
| Power transformer | 325-0-325 V · 6.3 V · 5 V | 5F1 Tweed Champ-style | HT + heaters + rectifier filament |
| Power transformer | HT (center-tapped) · 6.3 V · 5 V | 5F10 Tweed Harvard-style | HT + heaters + rectifier filament (no part number on the drawing) |
| Power transformer | HT c.t. · 6.3 V · 5 V | 5F2-A Tweed Princeton-style | Part 66079; HT winding voltage not printed on the drawing |
| Power transformer | Fender 8087 | 5F4 Tweed Super-style | HT + heaters + rectifier filament |
| Power transformer | Fender 8087 · 325-0-325 V | 5F6-A Tweed Bassman-style | HT + heaters + rectifier filament |
| Power transformer | Fender 125P33A · 330-0-330 V | AB763 Blackface Deluxe Reverb-style | HT + heaters + rectifier filament |
| Power transformer | 360-0-360 V HT · 6.3 V heaters | JTM45 British lead-style | HT + heaters + rectifier filament |
| Power transformer | Universal primary 110/120/200/225/245 V · HT + 6.3 V heaters | M1987 Plexi lead 50-style | Mains/HT transformer |
| Output transformer | ≈5 kΩ : 8 Ω | 5E1 Tweed Champ-style | Single-ended output (impedance not marked on the drawing; typical SE 6V6 load) |
| Output transformer | 8 kΩ : 8 Ω | 5E3 Tweed Deluxe-style | Push-pull output |
| Output transformer | ≈5 kΩ : 8 Ω | 5F1 Tweed Champ-style | Single-ended output (impedance not marked on the drawing; typical SE 6V6 load) |
| Output transformer | Push-pull (impedance ratio not printed on the drawing) | 5F10 Tweed Harvard-style | Push-pull output into the speaker |
| Output transformer | ≈ 5 kΩ : 8 Ω | 5F2-A Tweed Princeton-style | Single-ended output (part 265; impedance not marked on the drawing; typical SE 6V6 load) |
| Output transformer | Fender 45216 | 5F4 Tweed Super-style | Push-pull output into 2 × 10 in speakers |
| Output transformer | Fender 45249 · 2 Ω secondary | 5F6-A Tweed Bassman-style | Push-pull output into four 8 Ω speakers |
| Output transformer | Fender 125A1A | AB763 Blackface Deluxe Reverb-style | Push-pull 6V6 output |
| Output transformer | Push-pull, KT66 primary | JTM45 British lead-style | Push-pull output to the speaker |
| Output transformer | Push-pull EL34 primary, 16/8/4 Ω secondary | M1987 Plexi lead 50-style | Output transformer |
| Filter choke | ≈350 Ω DCR | 5E1 Tweed Champ-style | B+1→B+2 filter (DCR estimated; not marked on the drawing) |
| Filter choke | Fender 14684 | 5F4 Tweed Super-style | B+1 → B+2 (screens) |
| Filter choke | Fender 14684 | 5F6-A Tweed Bassman-style | B+1 → B+2 (screens) |
| Filter choke | Fender 125C3A | AB763 Blackface Deluxe Reverb-style | Reservoir → screen rail |
| Filter choke | 20 H | JTM45 British lead-style | B+1 → B+2 (screens) |
| Filter choke | 0.5 A | M1987 Plexi lead 50-style | Reservoir → screen-supply choke |
| Reverb transformer | Fender 125A20B | AB763 Blackface Deluxe Reverb-style | Reverb driver → tank input |
An output transformer matches the high plate impedance of the output tubes to the low impedance of the speaker. The turns ratio does it, and the impedance ratio is that ratio squared:
N = √(Zpri / Zsec) · Zpri = Zsec × N²
So the 8 kΩ : 8 Ω output transformer in the 5E3 is a 1000 : 1 impedance ratio — about 31.6 : 1 turns. That also runs backwards: the plates only see 8 kΩ when an 8 Ω speaker is on the secondary. Drop to a 4 Ω load and the plates see 4 kΩ, which is why a speaker-impedance mismatch shifts the whole load line, not just the level.
Put your own numbers in — the amp builder calculators include a live output-transformer ratio tool. For the design theory behind the iron, see Reuben Lee, Electronic Transformers and Circuits (1955).