Machine-checked wiring. Every modelled part the operating-point netlist places on this board — the tube sockets, the plate, cathode and grid-leak resistors, the power-rail droppers, and the coupling and bypass capacitors whose two leads are both named DC nodes — has been verified in CI, terminal for terminal, to be electrically equivalent to the simulated netlist this circuit is verified against: the same net structure, no missing or extra connections. Parts outside that DC model — the volume / tone / mixer control-network internals, the negative-bias front end, and the heater chain, pilot lamp and power-transformer / rectifier AC side — are drawn from the cited sources but are not machine-checked; the CI report enumerates every one of their terminals so the boundary is explicit rather than silent. This diagram documents connectivity and part arrangement — it is not a dimensioned 1:1 build template. Board and part positions are drawn at diagram scale, and lead dress, grounding paths, and physical spacing all matter in a high-voltage chassis. If you build from it, verify every connection against the schematic above and the operating-point table below as you go.
Operating point vs. published chart
Chart values read from the published drawing — or, where the drawing carries no voltage chart, from the cited published measurements (never reproduced). Tolerances are this project's verification targets — tighter on power rails than the ±20% measurement convention Fender printed on its charts. Simulation matches every node within target — worst deviation 12.9%.
| Node | Chart | Tolerance | Note |
|---|---|---|---|
| BP2 | 295 V | ±15% | screens node (after the 5 kΩ dropper) |
| BP3 | 250 V | ±15% | preamp node (after the 22 kΩ dropper) |
| PAY1 | 140 V | ±20% | 12AY7 plate — Robinette: 110 V drop across 100k from 250 V |
| PAY2 | 140 V | ±20% | 12AY7 plate (second channel) |
| P2A | 167 V | ±20% | 12AX7 V2A plate — 83 V drop across 100k |
| PPI | 203 V | ±20% | cathodyne plate — 47 V drop across 56k |
| KPI | — | informational — cathodyne cathode (self-biased via 1.5 kΩ/56 kΩ stack) | |
| JPI | — | informational — grid-leak return junction | |
| KAY | — | informational — shared 12AY7 cathode | |
| K2A | — | informational — V2A cathode (1.5 k bias) | |
| K66 | 19 V | ±20% | shared 6V6 cathode, 250 Ω 5 W |
Tube-pin nodes are checked against the chart's own printed ±20% convention; power-rail nodes are held to tighter internal verification targets.
Parts list
Reference designators match the schematic above. The schematic draws one input jack per channel (the real chassis has four, sharing these grid resistors). Dropper wattages are not marked on the drawing.
| Ref | Part | Value / rating | Role |
|---|---|---|---|
| R1s | Carbon comp resistor | 68 kΩ · ½ W | Instrument-channel grid stopper |
| R2s | Carbon comp resistor | 68 kΩ · ½ W | Mic-channel grid stopper |
| RG1 | Carbon comp resistor | 1 MΩ · ½ W | Instrument input grid leak |
| RG2 | Carbon comp resistor | 1 MΩ · ½ W | Mic input grid leak |
| RL1 | Carbon comp resistor | 100 kΩ · ½ W | V1A plate load |
| RL2 | Carbon comp resistor | 100 kΩ · ½ W | V1B plate load |
| RK1 | Carbon comp resistor | 820 Ω · ½ W | Shared 12AY7 cathode bias |
| C10 | Electrolytic capacitor | 25 µF · 25 V | Shared 12AY7 cathode bypass |
| C1 | Coupling capacitor | 0.1 µF · 400 V | V1A → instrument volume |
| C2 | Coupling capacitor | 0.1 µF · 400 V | V1B → mic volume |
| VR1 | Audio-taper potentiometer | 1 MΩ | Instrument volume |
| VR2 | Audio-taper potentiometer | 1 MΩ | Mic volume |
| RL3 | Carbon comp resistor | 100 kΩ · ½ W | V2A plate load |
| RK2 | Carbon comp resistor | 1.5 kΩ · ½ W | V2A cathode bias |
| C4 | Electrolytic capacitor | 25 µF · 25 V | V2A cathode bypass |
| C5 | Mica capacitor | 500 pF | Tone — treble path |
| VR3 | Audio-taper potentiometer | 1 MΩ | Tone |
| C6 | Film capacitor | 0.005 µF · 600 V | Tone — cut path to ground |
| RL4 | Carbon comp resistor | 56 kΩ · ½ W | Cathodyne plate load |
| RKA | Carbon comp resistor | 1.5 kΩ · ½ W | Cathodyne bias (cathode → junction) |
| RKB | Carbon comp resistor | 56 kΩ · ½ W | Cathodyne cathode load (junction → ground) |
| RGPI | Carbon comp resistor | 1 MΩ · ½ W | Cathodyne grid leak, returned to the junction |
| C7 | Coupling capacitor | 0.1 µF · 400 V | Cathodyne plate → V3 grid |
| C8 | Coupling capacitor | 0.1 µF · 200 V | Cathodyne cathode → V4 grid |
| R3s | Carbon comp resistor | 1.5 kΩ · ½ W | V3 grid stopper |
| R4s | Carbon comp resistor | 1.5 kΩ · ½ W | V4 grid stopper |
| RG6A | Carbon comp resistor | 220 kΩ · ½ W | V3 grid leak |
| RG6B | Carbon comp resistor | 220 kΩ · ½ W | V4 grid leak |
| RK66 | Wirewound resistor | 250 Ω · 5 W | Shared 6V6 cathode bias |
| C9 | Electrolytic capacitor | 25 µF · 25 V | Shared 6V6 cathode bypass |
| RD1 | Power resistor | 5 kΩ | Rail dropper B+1 → B+2 |
| RD2 | Power resistor | 22 kΩ | Rail dropper B+2 → B+3 |
| C11 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+1 |
| C12 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+2 |
| C13 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+3 |
| V1 | Preamp tube | 12AY7 | Both input stages (V1A/V1B) |
| V2 | Preamp tube | 12AX7 | Second stage + cathodyne (V2A/V2B) |
| V3 | Power tube | 6V6GT | Push-pull output (upper) |
| V4 | Power tube | 6V6GT | Push-pull output (lower) |
| V5 | Rectifier tube | 5Y3GT | Full-wave rectifier (V5A/V5B) |
| T2 | Output transformer | 8 kΩ : 8 Ω | Push-pull output |
| — | Power transformer | 325-0-325 V · 6.3 V · 5 V | HT + heaters + rectifier filament |
Circuit story
The most-built amp circuit in DIY history: two channels into a 12AY7, a 12AX7 second stage feeding the famous interactive volume/tone network, a cathodyne phase inverter, and a cathode-biased 6V6GT push-pull pair with no negative feedback — the recipe for tweed compression and breakup. Produced 1955–1960. Its direct ancestor, the 5D3, is not yet documented in this archive.
Circuit walkthrough (short form)
Two channels (each: 1M grid leak, 68k stoppers) → V1 12AY7 (100k plates, shared 820 Ω bypassed cathode) → 0.1 µF couplers → interactive 1M volume pots (+ single tone control: 500 pF/0.005 µF network) → V2A 12AX7 (100k plate, 1.5k bypassed cathode) → tone-cap coupling → V2B cathodyne phase inverter → 0.1 µF couplers → V3/V4 6V6GT pair (220k grid leaks, 1.5k stoppers, shared 250 Ω 5W bypassed cathode) → 8 kΩ : 8 Ω output transformer.
Power: 325-0-325 PT → 5Y3GT → three 16 µF/450 V nodes separated by 5,000 Ω and 22k droppers: B+1 (output plates) → B+2 (screens) → B+3 (preamp).
How the cathodyne biases itself
The 5E3's phase inverter uses a wiring detail that's easy to miss: V2B's cathode runs through 1.5k to a junction, then 56k to ground, and the 1M grid leak returns to that junction rather than to ground — the tone network's capacitors AC-couple the grid. The stage therefore biases itself: simulation puts the cathode at 45.8 V and the junction at 44.6 V — a clean −1.2 V bias — with the plate (56k from B+3) at 190 V.
Verification
Every component value comes from the published Fender drawing. The F-EE sheet carries no factory voltage chart (only Fender's ±20 % measurement notice), so this circuit is verified against the best published DC measurements instead: all seven reference nodes simulate within 13 % — rails within 8 %, stage plates within 13 %, and the 6V6 cathode within 8 %.