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 circuit's simulated netlist: 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.
| Node | Chart | Tolerance | Note |
|---|---|---|---|
| BP2 | 325 V | ±10% | 6V6 screen node, after the 10 kΩ dropper |
| BP3 | 250 V | ±10% | preamp node, after the 22 kΩ dropper |
| P1A | 170 V | ±20% | V1A 12AX7 plate, reference pin value |
| P1B | 170 V | ±20% | V1B 12AX7 plate (22k feedback on its cathode) |
| K2 | 19 V | ±20% | 6V6GT cathode across 470 Ω 1 W |
| K1A | — | informational — V1A cathode, ~1.5 V self-bias | |
| K1B | — | informational — V1B cathode; 22k speaker feedback parallels the 1.5k at DC |
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 5F2-A has one channel across two input jacks (high/low), each with its own 68 kΩ stopper sharing the 1 MΩ leak. V1B's cathode is deliberately UNbypassed — the 22 kΩ feedback resistor from the speaker works against it. Power transformer is listed at the end without a designator; its HT winding voltage is not printed on the drawing.
| Ref | Part | Value / rating | Role |
|---|---|---|---|
| R1 | Carbon comp resistor | 68 kΩ · ½ W | Input grid stopper, jack 1 (high) |
| R2 | Carbon comp resistor | 68 kΩ · ½ W | Input grid stopper, jack 2 (low) |
| R3 | Carbon comp resistor | 1 MΩ · ½ W | Input grid leak |
| R4 | Carbon comp resistor | 100 kΩ · ½ W | V1A plate load |
| R5 | Carbon comp resistor | 1.5 kΩ · ½ W | V1A cathode bias |
| R6 | Carbon comp resistor | 100 kΩ · ½ W | V1B plate load |
| R7 | Carbon comp resistor | 1.5 kΩ · ½ W | V1B cathode bias (unbypassed) |
| R8 | Carbon comp resistor | 220 kΩ · ½ W | 6V6 grid leak |
| R9 | Wirewound resistor | 470 Ω · 1 W | 6V6 cathode bias |
| R10 | Power resistor | 10 kΩ · 1 W | Rail dropper B+1→B+2 |
| R11 | Carbon comp resistor | 22 kΩ · ½ W | Rail dropper B+2→B+3 |
| R12 | Carbon comp resistor | 22 kΩ · ½ W | Negative feedback, speaker→V1B cathode |
| VR1 | Linear-taper potentiometer | 1 MΩ | Volume |
| VR2 | Linear-taper potentiometer | 1 MΩ | Tone |
| C1 | Electrolytic capacitor | 25 µF · 25 V | V1A cathode bypass |
| C2 | Coupling capacitor | 0.02 µF · 400 V | V1A → tone/volume network |
| C3 | Mica capacitor | 0.005 µF | Tone — treble shunt to ground |
| C4 | Mica capacitor | 500 pF | Tone — network to V1B grid |
| C5 | Coupling capacitor | 0.02 µF · 400 V | V1B → 6V6 grid |
| C6 | Electrolytic capacitor | 25 µF · 25 V | 6V6 cathode bypass |
| C7 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+1 |
| C8 | Electrolytic capacitor | 16 µF · 450 V | Filter, B+1 (paralleled) |
| C9 | Electrolytic capacitor | 8 µF · 450 V | Filter, B+2 |
| C10 | Electrolytic capacitor | 8 µF · 450 V | Filter, B+3 |
| C11 | Film capacitor | 0.05 µF · 600 V | Across the AC line |
| 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 (part 265; impedance not marked on the drawing; typical SE 6V6 load) |
| — | Power transformer | HT c.t. · 6.3 V · 5 V | Part 66079; HT winding voltage not printed on the drawing |
Circuit story
The tweed Princeton is the 5F1 Champ grown up: the same one-12AX7, single-ended 6V6 signal path, but with a tone control added and negative feedback wrapped around the driver stage. Five watts of the same sweet breakup, now with a treble knob and a firmer, more focused voice than the Champ's. Produced 1957–1961; its direct ancestor is the 5F2 not yet documented in this archive, and it is the tone-control-bearing sibling of the tweed Champ already in this archive.
One naming caution: later amps that carry the Princeton name are different circuits entirely — the brown 6G2 (1961 on) and the blackface Princeton and Princeton Reverb moved to a push-pull pair of 6V6s at roughly 12–15 W. This page documents the single-ended tweed 5F2-A only.
Circuit walkthrough (short form)
Two input jacks (high/low, each a 68 kΩ stopper sharing a 1 MΩ leak) → V1A (12AX7, 100 kΩ plate load, 1.5 kΩ bypassed cathode) → 0.02 µF coupling → tone/volume network → V1B (12AX7, 100 kΩ plate, 1.5 kΩ unbypassed cathode) → 0.02 µF coupling → V2 6V6GT (cathode-biased, 470 Ω 1 W, 220 kΩ grid leak) → single-ended output transformer → speaker.
The tone/volume network is a single interactive treble-cut: two 1 MΩ linear pots with a 0.005 µF shunt cap and a 500 pF series cap. It is entirely capacitor-coupled, so at DC V1B's grid simply returns to ground through the volume pot.
Negative feedback: 22 kΩ from the 8 Ω speaker output into V1B's cathode. Because that cathode is left unbypassed, the feedback has something to push against.
Power: the 66079 transformer → 5Y3GT full-wave → first node 32 µF (two 16 µF caps in parallel) at B+1 (6V6 plate) → 10 kΩ 1 W dropper → 8 µF B+2 (6V6 screen) → 22 kΩ dropper → 8 µF B+3 (both preamp plates).
The Champ with a backbone
Two small changes separate this circuit from the 5F1 and give the Princeton its character. First, V1B's cathode bypass capacitor is gone: the 5F1 bypasses that 1.5 kΩ for maximum gain, while the 5F2-A leaves it open so a global feedback loop can work against it. Second, that loop — 22 kΩ from the speaker back to the bare cathode — trades a little raw gain for a tighter, less compressed response and a touch more headroom. Add the treble-cut tone control and the result is an amp that cleans up and articulates where the Champ simply flatters.
At DC none of this changes the operating points: bypass caps and the whole tone network are invisible to a DC meter, so the 5F2-A idles exactly like a Champ. The one visible fingerprint of the feedback loop is that V1B's cathode sits a hair lower than V1A's — the 22 kΩ quietly parallels its 1.5 kΩ to ground.
Verification
The published K-EG drawing supplies every component value but prints no voltage chart — only Fender's standard ±20 % measurement notice. Because the 5F2-A's DC signal path is identical to the tweed 6V6 single-ended Champ (the tone control is capacitor-coupled and idles at nothing), simulation is checked against Rob Robinette's published DC measurements for that circuit: B+ 360 / 325 / 250 V, a ~19 V drop across the 6V6's 470 Ω cathode resistor, and 12AX7 plates near 170 V. Driving B+1 at 360 V, every compared node lands within about 8 %: the 6V6 cathode within about 2 % (19.4 V vs ~19 V, 2.1 %), the screen and preamp rails within 5–8 %, and both 12AX7 plates within 7 %.
The match is well inside Fender's ±20 % convention, but the reference is a sibling model rather than the 5F2-A itself — a different power transformer could shift the absolute B+ — so this circuit is published as a draft pending a voltage chart measured on a 5F2-A.