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 11.3%.
| Node | Chart | Tolerance | Note |
|---|---|---|---|
| BP2 | 410 V | ±8% | screens node after the choke (DCR estimated at 130 Ω) |
| BP3 | 332 V | ±8% | PI supply node after the first 10 kΩ dropper |
| BP4 | 280 V | ±8% | preamp node after the second 10 kΩ dropper |
| PAY1 | 140 V | ±20% | 12AY7 plate (channel 1) |
| PAY2 | 140 V | ±20% | 12AY7 plate (channel 2) |
| KAY | 2.2 V | ±20% | shared 12AY7 cathode, 820 Ω |
| P2A | 140 V | chart disputed | The printed pair (140 V plate, 2.2 V cathode) is physically impossible for a 12AX7: 2.2 V across 1.5 kΩ implies 1.47 mA, which at Vg ≈ −2.2 V requires roughly 280 V plate-to-cathode — twice the printed value. Philips' measured resistance-coupled tables and simulation both put the self-consistent point near 190 V. |
| K2A | 2.2 V | chart disputed | Half of the physically-impossible printed pair on V2A — see P2A. |
| KCF | 140 V | chart disputed | Direct-coupled to V2A's plate, so it inherits the disputed printed 140 V; simulation follows the self-consistent operating point near 190 V. |
| PPIA | 270 V | ±20% | PI plate, 56 kΩ side |
| PPIB | 213 V | chart disputed | Mutually inconsistent with the printed 270 V opposite plate and the tail arithmetic; simulation reproduces the 270 V side within tolerance. |
| KPI | 55 V | chart disputed | The printed 55 V cathodes and 53.3 V junction contradict the printed plate pair and the 1.5 kΩ/56 kΩ tail arithmetic; simulation settles where the same stage family measures in the 5F6-A. |
| JPI | 53.3 V | chart disputed | See KPI — the printed tail values contradict the printed plates. |
| G51 | -40 V | ±8% | 6L6G fixed bias via 220k from the -40 V supply |
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 jack per channel (the chassis has four). Output tubes are drawn '6L6G' on the C-EG sheet; Fender shipped the tweed Super with 5881s (interchangeable 6L6-family) and the 5881 SPICE model stands in for simulation. The treble/bass tone stack is capacitor-coupled and omitted from the DC netlist. Parts drawn only as annotations (bright cap, presence, NFB, line caps, power transformer) are listed without designators.
| Ref | Part | Value / rating | Role |
|---|---|---|---|
| R1s | Carbon comp resistor | 68 kΩ · ½ W | Channel-1 grid stopper |
| R2s | Carbon comp resistor | 68 kΩ · ½ W | Channel-2 grid stopper |
| RG1 | Carbon comp resistor | 1 MΩ · ½ W | Channel-1 input grid leak |
| RG2 | Carbon comp resistor | 1 MΩ · ½ W | Channel-2 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 |
| C3 | Electrolytic capacitor | 25 µF · 25 V | Shared 12AY7 cathode bypass |
| C1 | Coupling capacitor | 0.02 µF · 600 V | V1A → channel-1 volume |
| C2 | Coupling capacitor | 0.02 µF · 600 V | V1B → channel-2 volume |
| VR1 | Audio-taper potentiometer | 1 MΩ | Channel-1 volume (100 pF bright cap across it) |
| VR2 | Audio-taper potentiometer | 1 MΩ | Channel-2 volume |
| RM1 | Carbon comp resistor | 270 kΩ · ½ W | Channel-1 mixer |
| RM2 | Carbon comp resistor | 270 kΩ · ½ W | Channel-2 mixer |
| 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 |
| RKCF | Carbon comp resistor | 100 kΩ · ½ W | Cathode-follower load |
| RF1 | Carbon comp resistor | 4.7 MΩ · ½ W | V2A grid reference / feedback from the tone-stack output |
| RSL | Carbon comp resistor | 100 kΩ · ½ W | Tone-stack slope resistor |
| C5 | Mica capacitor | 250 pF | Tone stack — treble |
| VR3 | Potentiometer (taper not marked on the drawing) | 1 MΩ | Treble |
| C6 | Mica capacitor | 0.01 µF | Tone stack — treble bypass |
| C7 | Film capacitor | 0.005 µF | Tone stack — bass |
| VR4 | Audio-taper potentiometer | 1 MΩ | Bass |
| C8 | Coupling capacitor | 0.02 µF · 600 V | Tone stack → phase-inverter grid |
| RGA | Carbon comp resistor | 1 MΩ · ½ W | PI grid leak (V3A), returned to the tail junction |
| RGB | Carbon comp resistor | 1 MΩ · ½ W | PI grid leak (V3B), returned to the tail junction |
| RLA | Carbon comp resistor | 56 kΩ · ½ W | PI plate load (V3A) |
| RLB | Carbon comp resistor | 100 kΩ · ½ W | PI plate load (V3B) |
| RTAIL | Carbon comp resistor | 1.5 kΩ · ½ W | PI tail (cathodes → junction) |
| RT2 | Carbon comp resistor | 56 kΩ · ½ W | PI tail (junction → ground) |
| C9 | Coupling capacitor | 0.1 µF · 400 V | PI → V4 grid |
| C10 | Coupling capacitor | 0.1 µF · 200 V | PI → V5 grid |
| R5s | Carbon comp resistor | 1.5 kΩ · ½ W | V4 grid stopper |
| R6s | Carbon comp resistor | 1.5 kΩ · ½ W | V5 grid stopper |
| RGL1 | Carbon comp resistor | 220 kΩ · ½ W | V4 grid leak, from the −40 V bias line |
| RGL2 | Carbon comp resistor | 220 kΩ · ½ W | V5 grid leak, from the −40 V bias line |
| RD1 | Power resistor | 10 kΩ | Rail dropper B+2 → B+3 |
| RD2 | Power resistor | 10 kΩ | Rail dropper B+3 → B+4 |
| L1 | Filter choke | Fender 14684 | B+1 → B+2 (screens) |
| C11 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+1 (reservoir) |
| C12 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+2 |
| C13 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+3 |
| C14 | Electrolytic capacitor | 8 µF · 450 V | Filter, B+4 |
| D1 | Rectifier (bias) | selenium (silicon diode in modern builds) | Bias supply rectifier |
| RB1 | Carbon comp resistor | 6.8 kΩ · ½ W | Bias supply series resistor |
| RB2 | Carbon comp resistor | 56 kΩ · ½ W | Bias supply bleeder |
| C15 | Electrolytic capacitor | 8 µF · 150 V | Bias supply filter |
| V1 | Preamp tube | 12AY7 | Both input stages (V1A/V1B) |
| V2 | Preamp tube | 12AX7 | Gain stage + cathode follower (V2A/V2B) |
| V3 | Preamp tube | 12AX7 | Long-tailed-pair phase inverter (V3A/V3B) |
| V4 | Power tube | 6L6G | Push-pull output (upper) |
| V5 | Power tube | 6L6G | Push-pull output (lower) |
| V6 | Rectifier tube | 5U4G | Full-wave rectifier (V6A/V6B) |
| T3 | Output transformer | Fender 45216 | Push-pull output into 2 × 10 in speakers |
| — | Power transformer | Fender 8087 | HT + heaters + rectifier filament |
| — | Mica capacitor | 100 pF | Bright cap across VR1 (annotation only on schematic) |
| — | Linear potentiometer | 5 kΩ | Presence (annotation only) |
| — | Carbon comp resistor | 56 kΩ · ½ W | Negative feedback, speaker → PI tail (annotation only) |
| — | Film capacitor | 0.05 µF · 600 V (×2) | AC-line filter caps (annotation only) |
Circuit story
The tweed Super is the Bassman's guitar-voiced sibling: the same big-bottle preamp architecture — a 12AY7 two-channel front end, a 12AX7 gain stage feeding a direct-coupled cathode follower, a treble/bass tone stack, a long-tailed-pair phase inverter, and a fixed-bias pair of 6L6-family output tubes — but built around two 10-inch speakers instead of the Bassman's four tens. Produced across the late-tweed years (1957–1960), it shares the 5F6-A's power section almost part-for-part (PT 8087, choke 14684, a 5881/6L6G pair biased near −40 V) while running a slightly lower rail set. Its direct ancestor is the 5E-series Super not yet published in this archive.
Circuit walkthrough (short form)
Two channels (each: 1M grid leak, 68k stopper) → V1 12AY7 (100k plates, shared 820 Ω cathode with 25 µF bypass) → 0.02 µF couplers → 1M volume pots → 270k mixers → V2A 12AX7 (100k plate, 1.5k/25 µF cathode) → V2B cathode follower, DC-coupled (100k cathode load) → treble/bass tone stack (100k slope, 250 pF treble cap, 1M treble and bass pots) → 0.02 µF → long-tailed-pair PI: 56k and 100k plates, 1.5k + 56k tail, both 1M grid leaks returned to the tail junction → 0.1 µF couplers → 6L6G pair, fixed-biased at −40 V through 220k leaks, screens tied straight to the +410 V node → Fender 45216 output transformer into the two 10-inch speakers, with a 56k negative-feedback loop and a 5k presence control.
Power: 5U4G rectifier → +415 V reservoir (output plates) → choke (14684) → +410 V screens → 10k → +332 V phase-inverter supply → 10k → +280 V preamp. A selenium rectifier with a 6.8k/56k network supplies the −40 V bias.
The output tubes are lettered 6L6G on the C-EG sheet; Fender equipped the tweed Super with 5881s, the ruggedized 6L6 the Bassman and Twin also used, and the two are interchangeable. Simulation here uses the 6L6-family 5881 model.
The elevated phase-inverter tail
The long-tailed pair biases itself well up off ground. The two cathodes sit near +55 V, joined through a 1.5k resistor to a junction at +53.3 V, which then reaches ground through 56k. Both grid-leak resistors (1M each) return to that +53.3 V junction rather than to ground, so each grid rides up close to its own cathode and the tubes see only a volt or two of bias — the classic Fender trick that lets a single 12AX7 swing both output tubes symmetrically. The 56k feedback resistor and the 5k presence pot join the tail circuit but sit at roughly 0 V DC through the speaker winding, so they do not move the operating point.
Verification — and what the chart gets wrong
The rails, the 12AY7 front end, the phase inverter's 56 kΩ-side plate, and the 6L6 fixed-bias supply all verify against the printed chart (worst node 11.3 %, against the chart's own ±20 % convention). Six printed values are excluded as disputed, with the arithmetic shown in the voltage table: the chart's V2A pair (140 V plate with a 2.2 V cathode) is physically impossible for a 12AX7 — that cathode voltage implies a current the tube can only pass near 280 V — and its phase-inverter figures contradict each other. Measured period data and simulation agree the real operating point sits near 190 V. The full analysis is in the archive's 12AX7 calibration study.