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 — 82 transformers and 22 chokes across 39 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 | 5C1 Wide-panel Champ-style | HT secondary (voltage not marked; +340 V reservoir implies ≈345-0-345) + heater and rectifier windings |
| Power transformer | centre-tapped HT · 6.3 V · 5 V (voltages not marked) | 5D3 Wide-panel Tweed Deluxe-style | HT + heaters + rectifier filament |
| 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 | HT · 6.3 V heaters · 5 V rectifier filament | 5E4-A Tweed Super-style | Mains/HT transformer |
| Power transformer | ~330-0-330 V · 6.3 V · 5 V (est.) | 5E5-A Tweed Pro-style | HT + heaters + rectifier filament |
| Power transformer | Fender part number not legible on this scan | 5E6-A Tweed Bassman-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 Tweed Bassman-style | HT + heaters + rectifier filament |
| Power transformer | Fender 8087 · 325-0-325 V | 5F6-A Tweed Bassman-style | HT + heaters + rectifier filament |
| Power transformer | Valco E-3693A | 6161 Valco 6161-style | Mains transformer — centre-tapped HT winding (grounded), 5 V rectifier winding, 6.3 V heater winding. The drawing prints the part number and no winding voltages |
| Power transformer | 125P1A | 6G2 Brown Princeton-style | HT + heaters + rectifier filament |
| Power transformer | 125P2A · 333-0-333 V · 6.3 V · 5 V | 6G3 Brown Deluxe-style | HT + heaters + rectifier filament |
| Power transformer | Fender 8087 | 6G4 Brown Super-style | HT + heaters + rectifier filament |
| Power transformer | HT secondary · 6.3 V heaters | 6G5 Brown Pro-style | Mains primary + HT/heater secondaries; no part number printed on this sheet |
| Power transformer | Fender 125P7A (TR1) | 6G6-B Blonde Bassman-style | HT + heaters, centre-tapped HT winding for the solid-state bridge |
| Power transformer | Fender 125P1B · 340-0-340 V | AA1164 Blackface Princeton Reverb-style | HT + heaters + rectifier filament |
| Power transformer | Fender 125P1B · 320-0-320 V · 6.3 V · 5 V | AA764 Blackface Champ-style | HT + heaters + rectifier filament |
| Power transformer | Fender 125P1B · 315-0-315 V · 6.3 V · 5 V | AA764 (Vibro Champ-style) Blackface Vibro Champ-style | HT + heaters + rectifier filament |
| Power transformer | Fender 125P7D · 305-0-305 V AC | AA864 (Bassman-style) Blackface Bassman-style | HT + heaters + pilot (export model: 125P7DX) |
| Power transformer | Fender 125P1B · 340-0-340 V | AA964 Blackface Princeton-style | HT + heaters + rectifier filament |
| Power transformer | Fender 125P7D · 320-0-320 V | AB165 Blackface Bassman-style | HT + heaters (export model 125P7DX) |
| Power transformer | Fender 125P33A · 330-0-330 V | AB763 Blackface Deluxe Reverb-style | HT + heaters + rectifier filament |
| Power transformer | Fender 125P5D · 360-0-360 V | AB763 (Super Reverb-style) Blackface Super Reverb-style | HT + heaters + bias tap + rectifier filament |
| Power transformer | Fender 125P34A · 340-0-340 V | AB763 (Twin Reverb-style) Blackface Twin Reverb-style | HT (with bias tap) + 6.3 V heaters |
| Power transformer | Haddon OF 031 · HT secondary 300-0-300 V at 130 mA · 6.3 V, 4 A heater winding · primary taps 115/160/205/225/245 V | AC15 Vox AC15-style | Mains/HT transformer |
| Power transformer | HT secondary 280-0-280 V at 160 mA · 6.3 V, 6 A heater winding · 5 V, 2 A rectifier winding · primary taps 115/160/205/225/245 V | AC30 Vox AC30/6-style | Mains/HT transformer (Haddon) |
| Power transformer | Ampeg PT-108 (300708-1) | B15N Ampeg B-15N Portaflex-style | Mains transformer — centre-tapped HT winding, 5 V rectifier winding, 6.3 V heater winding. The drawing prints the part number and no winding voltages |
| Power transformer | Hiwatt TH7548/5 · 100/117.5/225/250 V primary taps | DR103 Hiwatt Custom 100-style | Mains/HT transformer with the bias winding (annotation) |
| Power transformer | Gibson (no number printed) | GA40 Gibson GA-40 Les Paul-style | Mains transformer — centre-tapped HT winding, 5 V rectifier winding, 6.3 V heater winding. The drawing prints the windings and no part number |
| Power transformer | 110/250 V universal primary · HT + 6.3 V heaters | JTM100 British 100-watt lead-style | HT and heater supply |
| 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 | M1959 Super Lead 100-style | Mains/HT transformer |
| Power transformer | Universal primary 110/120/200/225/245 V · HT + 6.3 V heaters | M1987 Plexi lead 50-style | Mains/HT transformer |
| Power transformer | Marshall 1202-324 · 240/220/120 V primary · HT + 6.3 V heaters | M2204 Master Volume lead 50-style | Mains/HT transformer |
| Power transformer | Sears DD-50 | S1484 Silvertone Twin Twelve-style | Mains transformer, 117 V 60 Hz. The drawing prints winding RESISTANCES rather than voltages: 3.7 Ω primary, 5.75 Ω and 6.2 Ω on the two HT windings that feed the multiplier, 3.7 Ω on the bias winding, plus the 6.3 V heater winding |
| Output transformer | ≈5 kΩ : 8 Ω | 5C1 Wide-panel Champ-style | Single-ended output (impedance not marked on the drawing; typical SE 6V6 load) |
| Output transformer | push-pull : 8 Ω | 5D3 Wide-panel Tweed Deluxe-style | Push-pull output, with a second 8 Ω jack for an extra speaker; the drawing marks no impedances |
| 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 | push-pull output transformer | 5E4-A Tweed Super-style | Push-pull output into 2 × 10 in speakers, with an external-speaker jack |
| Output transformer | ~4.3 kΩ : 8 Ω (est. for 2x6L6GB into one 15" speaker) | 5E5-A Tweed Pro-style | Push-pull output |
| Output transformer | Fender part number not legible on this scan | 5E6-A Tweed Bassman-style | Push-pull output into four 10-inch speakers |
| 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 Tweed Bassman-style | Push-pull output into four 8 Ω speakers |
| Output transformer | Fender 45249 · 2 Ω secondary | 5F6-A Tweed Bassman-style | Push-pull output into four 8 Ω speakers |
| Output transformer | Valco 340-6 | 6161 Valco 6161-style | Output transformer, centre-tapped primary; the centre tap is the reservoir node |
| Output transformer | 125A10B | 6G2 Brown Princeton-style | Push-pull output, centre-tapped primary |
| Output transformer | 125A1A | 6G3 Brown Deluxe-style | Push-pull output |
| Output transformer | Fender 45216 | 6G4 Brown Super-style | Push-pull 6L6GC output |
| Output transformer | push-pull : speaker | 6G5 Brown Pro-style | Push-pull output into the 15-inch speaker; no part number printed on this sheet |
| Output transformer | Fender 125A13A | 6G6-B Blonde Bassman-style | Push-pull output |
| Output transformer | Fender 125A10B | AA1164 Blackface Princeton Reverb-style | Push-pull 6V6 output |
| Output transformer | Fender 125A35A | AA764 Blackface Champ-style | Single-ended output (impedance ratio not marked on the drawing) |
| Output transformer | Fender 125A35A | AA764 (Vibro Champ-style) Blackface Vibro Champ-style | Single-ended output (impedance ratio not marked on the drawing) |
| Output transformer | Fender 125A13A | AA864 (Bassman-style) Blackface Bassman-style | Push-pull 6L6GC output, into the 2x12 cabinet + EXT SPKR jack |
| Output transformer | Fender 125A10B | AA964 Blackface Princeton-style | Push-pull 6V6 output |
| Output transformer | Fender 125A13A | AB165 Blackface Bassman-style | Push-pull 6L6GC output |
| Output transformer | Fender 125A1A | AB763 Blackface Deluxe Reverb-style | Push-pull 6V6 output |
| Output transformer | Fender 125A9A | AB763 (Super Reverb-style) Blackface Super Reverb-style | Push-pull 6L6GC output |
| Output transformer | Fender 125A29A | AB763 (Twin Reverb-style) Blackface Twin Reverb-style | Parallel push-pull primary for four 6L6GC; 4 Ω secondary into two speakers, with the feedback tap |
| Output transformer | Haddon OA 063 · push-pull EL84 primary · 8 Ω / 15 Ω secondary taps | AC15 Vox AC15-style | Output transformer |
| Output transformer | 4 kΩ anode-to-anode primary · 8 Ω / 15 Ω secondary taps | AC30 Vox AC30/6-style | Output transformer (Haddon) |
| Output transformer | Ampeg OT-214 | B15N Ampeg B-15N Portaflex-style | Push-pull 6L6GC output, centre-tapped primary (blue/red/brown), tapped secondary (green/yellow/black); the handwritten part number beside it is only partly legible on this scan |
| Output transformer | Hiwatt TH7549/2 · 4/8/16 Ω taps | DR103 Hiwatt Custom 100-style | Output transformer, feedback from the 16 Ω tap; the Reeves-era four-input heads carried Partridge iron whose DR103 part number was not read on any drawing consulted |
| Output transformer | Gibson (no number printed) | GA40 Gibson GA-40 Les Paul-style | Output transformer, centre-tapped primary; the centre tap is the post-choke supply node the screens also sit on |
| Output transformer | Push-pull, 4x KT66 primary | JTM100 British 100-watt lead-style | Output to the speaker; secondary leads lettered on the sheet — blue 100 V line, white 16 Ω, yellow 8 Ω, orange common |
| Output transformer | Push-pull, KT66 primary | JTM45 British lead-style | Push-pull output to the speaker |
| Output transformer | 16/8/4 Ω taps | M1959 Super Lead 100-style | Output transformer — parallel push-pull primary for four EL34s, 16/8/4 Ω secondary taps (feedback from the 16 Ω tap) |
| Output transformer | Push-pull EL34 primary, 16/8/4 Ω secondary | M1987 Plexi lead 50-style | Output transformer |
| Output transformer | Marshall 789-139 · 16/8/4 Ω taps | M2204 Master Volume lead 50-style | Push-pull EL34 output transformer |
| Output transformer | Sears O50 | S1484 Silvertone Twin Twelve-style | Output transformer, centre-tapped primary; the drawing prints 85 Ω for each primary half and takes the centre tap to the 480 V rail. Secondary drives two 8 Ω speakers |
| Filter choke | ≈350 Ω DCR | 5E1 Tweed Champ-style | B+1→B+2 filter (DCR estimated; not marked on the drawing) |
| Filter choke | filter choke | 5E4-A Tweed Super-style | B+1 → B+2 (screens and output-transformer centre tap) |
| Filter choke | ~110 Ω DCR (est.) | 5E5-A Tweed Pro-style | BP1 → BP2, screens supply |
| Filter choke | Fender 14684 | 5F4 Tweed Super-style | B+1 → B+2 (screens) |
| Filter choke | Fender 14684 | 5F6 Tweed Bassman-style | B+1 → B+2 (screens) |
| Filter choke | Fender 14684 | 5F6-A Tweed Bassman-style | B+1 → B+2 (screens) |
| Filter choke | Fender 125C1A | 6G4 Brown Super-style | Reservoir → screen/preamp rail |
| Filter choke | Fender 125C1A (TR2) | 6G6-B Blonde Bassman-style | B+ filtering |
| Filter choke | Fender 125C1A | AA864 (Bassman-style) Blackface Bassman-style | Plate rail → screen rail |
| Filter choke | Fender 125C1A | AB165 Blackface Bassman-style | Reservoir → screen rail |
| Filter choke | Fender 125C3A | AB763 Blackface Deluxe Reverb-style | Reservoir → screen rail |
| Filter choke | Fender 125C1A | AB763 (Super Reverb-style) Blackface Super Reverb-style | Reservoir → 6L6GC plate/screen rail |
| Filter choke | Fender 125C1A | AB763 (Twin Reverb-style) Blackface Twin Reverb-style | Reservoir → screen/post-choke node [B] |
| Filter choke | Radiospares OA 123 · 10–20 H · 100 mA DC | AC15 Vox AC15-style | Smoothing choke between reservoir and HT rail |
| Filter choke | 10–20 H · 100 mA DC | AC30 Vox AC30/6-style | Smoothing choke between reservoir and HT rail (Radiospares) |
| Filter choke | 20 H | JTM100 British 100-watt lead-style | Reservoir → KT66 screen node |
| 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 |
| Filter choke | choke (value not marked) | M2204 Master Volume lead 50-style | Reservoir → screen-supply choke |
| Choke | CH. · inductance not printed | 6G5 Brown Pro-style | B+ reservoir to plates/screens filter choke, labelled CH. on the drawing |
| Reverb transformer | Fender 125A20B | AA1164 Blackface Princeton Reverb-style | Reverb driver → tank input |
| Reverb transformer | Fender 125A20B | AB763 Blackface Deluxe Reverb-style | Reverb driver → tank input |
| Reverb transformer | Fender 125A20B | AB763 (Super Reverb-style) Blackface Super Reverb-style | Reverb driver → tank input |
| Reverb transformer | Fender 125A20B | AB763 (Twin Reverb-style) Blackface Twin Reverb-style | Reverb driver → tank input |
| Choke | 3 H | GA40 Gibson GA-40 Les Paul-style | Smoothing choke between the reservoir and the screen/output-transformer node |
| Choke | Sears L480 | S1484 Silvertone Twin Twelve-style | Supply choke, between a junction of the capacitor-multiplier stack and the 340 V screen node. The drawing prints no inductance and no DC resistance |
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).