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 14.9%.
| Node | Chart | Tolerance | Note |
|---|---|---|---|
| BP2 | 295 V | ±5% | 6V6 screen node, after the 10 kΩ dropper (R10) |
| BP3 | 250 V | ±5% | preamp node, after the 22 kΩ dropper (R11) |
| P1A | 150 V | ±20% | 12AX7 plate, chart pin value |
| P1B | 150 V | ±20% | 12AX7 plate, chart pin value |
| K1A | 1.5 V | ±20% | 12AX7 cathode, chart pin value |
| K1B | 1.5 V | ±20% | 12AX7 cathode (NFB 22k parallels at DC) |
| K2 | 18 V | ±20% | 6V6GT cathode, chart pin 8 |
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. Numbering follows the schematic; gaps (R2, R12, …) are intentional. Power transformer and chassis hardware are listed at the end without designators.
| Ref | Part | Value / rating | Role |
|---|---|---|---|
| R1 | Carbon comp resistor | 1 MΩ · ½ W | Input grid leak |
| R3 | Carbon comp resistor | 68 kΩ · ½ W | Input grid stopper |
| R4 | Carbon comp resistor | 1.5 kΩ · ½ W | V1A cathode bias |
| R5 | Carbon comp resistor | 100 kΩ · ½ W | V1A plate load |
| R6 | Carbon comp resistor | 1.5 kΩ · ½ W | V1B cathode bias |
| R7 | Carbon comp resistor | 100 kΩ · ½ W | V1B plate load |
| R8 | Wirewound resistor | 470 Ω · 5 W | 6V6 cathode bias |
| R9 | Carbon comp resistor | 220 kΩ · ½ W | 6V6 grid leak |
| R10 | Power resistor | 10 kΩ · 2 W | Rail dropper B+1→B+2 |
| R11 | Power resistor | 22 kΩ · 2 W | Rail dropper B+2→B+3 |
| R13 | Carbon comp resistor | 22 kΩ · ½ W | Negative feedback, speaker→V1B cathode |
| VR1 | Audio-taper potentiometer | 1 MΩ | Volume |
| C1 | Coupling capacitor | 0.02 µF · 600 V | V1A → volume |
| C2 | Electrolytic capacitor | 25 µF · 25 V | V1A cathode bypass |
| C3 | Coupling capacitor | 0.02 µF · 600 V | V1B → 6V6 grid |
| C4 | Electrolytic capacitor | 25 µF · 25 V | V1B cathode bypass |
| C5 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+1 |
| C6 | Electrolytic capacitor | 25 µF · 25 V | 6V6 cathode bypass |
| C7 | Electrolytic capacitor | 8 µF · 450 V | Filter, B+2 |
| C8 | Electrolytic capacitor | 8 µF · 450 V | Filter, B+3 |
| V1 | Preamp tube | 12AX7 | Both gain stages (V1A/V1B) |
| V2 | Power tube | 6V6GT | Single-ended output |
| V3 | Rectifier tube | 5Y3GT | Full-wave rectifier (V3A/V3B) |
| T2 | Output transformer | ≈5 kΩ : 8 Ω | Single-ended output (impedance not marked on the drawing; typical SE 6V6 load) |
| — | Power transformer | 325-0-325 V · 6.3 V · 5 V | HT + heaters + rectifier filament |
Circuit story
The smallest amp in the tweed canon and the clearest illustration of a complete
guitar amplifier: one 12AX7 providing two gain stages, a cathode-biased 6V6GT
single-ended output, a 5Y3GT rectifier, and nothing else — no tone control, no
phase inverter, five watts of pure signal path. Produced 1958–1964; direct
ancestor: the 5E1 (lineage edge lands when amps/5e1 exists).
Circuit walkthrough (short form)
Input jack → 68k grid stopper → V1A (12AX7, 100k plate load, 1.5k bypassed cathode) → 0.02 µF coupling → 1M audio volume pot → V1B (12AX7, 100k plate, 1.5k cathode) → 0.02 µF coupling → V2 6V6GT (cathode-biased, 470 Ω 5 W, 220k grid leak) → single-ended output transformer (≈5 kΩ : 8 Ω, typical for a single-ended 6V6; the drawing doesn't mark it) → speaker. Negative feedback: 22k from the speaker jack into V1B's cathode (at DC this parallels the 1.5k through the secondary's near-zero DCR).
Power: 325-0-325 PT → 5Y3GT full-wave → filter nodes 16 µF / 8 µF / 8 µF (450 V) separated by a 10k and a 22k dropper (all confirmed in print on the K-EE sheet): B+1 340 V (output plate) → B+2 295 V (screen) → B+3 250 V (preamp plates).
How simulation pinned down the rail dropper
The published chart marks B+1 340 V, B+2 295 V, B+3 250 V. Driving B+1 at 340 V, simulation discriminates the second dropping-resistor value cleanly — a nice example of what simulation-verified archiving can do:
| Node | Chart | Sim with 10k | Sim with 22k |
|---|---|---|---|
| B+2 | 295 V | 291 V (1.3%) | 291.5 V (1.2%) |
| B+3 | 250 V | 273 V (9.2% off) | 252 V (0.8%) |
With 22k, the downstream stage voltages fall into line as well. Conclusion: the second dropper is 22k — a value some descriptions of this circuit get wrong — and the schematic's printed 22K marking confirms it.
Verification
Simulation is checked against the drawing's full printed voltage chart: the 6V6 cathode within 0.2 % (18.0 V vs +18 V), rails within 1.2 %, and the 12AX7 pins (+150 V plate, +1.5 V cathode) within the chart's own printed ±20 % convention — Fender measured on 1958 production tubes, while these models are datasheet-typical, so the preamp simulating slightly leaner than the era measurement is expected behavior. Planned refinements: output-transformer primary resistance in the DC deck, and full curve-traced tube models.