5E1 Tweed Champ‑style · 1955–1957 · 5 W

✓ verified 2026-07-18
Schematic — redrawn in KiCad · scroll to zoom, drag to pan
Board layout — redrawn reference diagram · source noted on the drawing Print sheet ↗
5E1 eyelet board layout — an original diagram redrawn from the published layout drawing, showing the principal parts in the order that drawing places them on the board, drawn in the period layout-sheet style with each value lettered on the part.

Scroll the drawing sideways to read the whole board — the source line and the colour legend run along the bottom of the sheet — or open the full-size diagram in its own tab. Values are lettered on the parts in the period shorthand — .02-400, 250-5, 1MEG: how to read it.

Machine-checked wiring. Every modelled part the operating-point netlist places on this board has been verified in CI, terminal for terminal, to be electrically equivalent to the simulated netlist this circuit is verified against. This diagram documents connectivity and part arrangement — it is not a dimensioned 1:1 build template.

Details

The modelled parts are 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; the check proves the same net structure, with 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.

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). The simulated column is this circuit's own netlist solved in ngspice by the run that gates it; every deviation beside it is those two numbers compared, not a separately stated figure. Tolerances are this project's verification targets: tube-pin nodes carry the tolerance the cited source states, or ±20% — the era's printed convention — where it states none, and power rails are held to tighter internal targets. Every gated node lands within target — worst deviation 14.7%.

Node Chart Simulated Deviation Tolerance Note
BP2 305 V 305.2 V 0.1% ±8% output B+ after the choke — 6V6 plate (via OT) and screen
BP3 260 V 264.1 V 1.6% ±8% preamp node after the 22 kΩ dropper
P1A 150 V 172.1 V 14.7% ±20% 12AX7 V1A plate, chart pin value
P1B 150 V 169.3 V 12.9% ±20% 12AX7 V1B plate, chart pin value
K1A 1.5 V 1.4 V 8.0% ±20% 12AX7 V1A cathode, chart pin value (bypassed 25 µF)
K1B 1.5 V 1.3 V 11.3% ±20% 12AX7 V1B cathode (unbypassed; NFB 22k parallels at DC)
K2 19 V 19.0 V 0.1% ±20% 6V6GT cathode, chart pin value (470 Ω, 25 µF bypass)

Tube-pin nodes are checked at the tolerance the cited source states, or at the era's ±20% convention where it states none; power-rail nodes are held to tighter internal verification targets. Simulated figures are the netlist's DC solution, not measurements from a chassis.

The output stage behind these numbers can be drawn: the load line explorer plots this circuit's 6V6GT at the DC operating point its netlist carries — 305 V on the plates with a 470 Ω cathode resistor — and marks where the load line crosses.

Parts list

Every designator in this list appears on the schematic above, and every designator on the schematic appears here — the two are checked against each other in both directions, a valve's two halves counting as one bottle (V1A and V1B are both V1). Three parts the drawing carries as annotations rather than numbered symbols are listed here without designators, and stand outside that check. Numbering follows the schematic. The AC-line section (power transformer, fuse, line cap) is drawn as annotation only and carries no designator. Values are from the published Champ 5E1 (H-EE) drawing.

RefPartValue / ratingRole
R1 Carbon comp resistor 68 kΩ · ½ W Input 1 grid stopper
R2 Carbon comp resistor 68 kΩ · ½ W Input 2 grid stopper
R3 Carbon comp resistor 1 MΩ · ½ W Grid leak
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 22 kΩ · 1 W Rail dropper B+2→B+3
R11 Carbon comp resistor 22 kΩ · ½ W Negative feedback, speaker→V1B cathode
VR1 Audio-taper potentiometer 1 MΩ Volume
C1 Electrolytic capacitor 25 µF · 25 V V1A cathode bypass
C2 Coupling capacitor 0.02 µF · 600 V V1A → volume
C3 Coupling capacitor 0.02 µF · 600 V V1B → 6V6 grid
C4 Electrolytic capacitor 25 µF · 25 V 6V6 cathode bypass
C5 Electrolytic capacitor 8 µF · 450 V Filter, B+1 (reservoir)
C6 Electrolytic capacitor 8 µF · 450 V Filter, B+2
C7 Electrolytic capacitor 8 µF · 450 V Filter, B+3
L1 Filter choke ≈350 Ω DCR B+1→B+2 filter (DCR estimated; not marked on the drawing)
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)
T1 Output transformer ≈5 kΩ : 8 Ω Single-ended output (impedance not marked on the drawing; typical SE 6V6 load)
Power transformer HT · 6.3 V · 5 V HT secondary (voltage not marked; +320 V reservoir implies ≈325-0-325) + heater and rectifier windings
Line capacitor 0.05 µF · 600 V Across the AC line at the fuse
Fuse 2 A AC-line fuse

Circuit story

The mid-1950s tweed Champ: a single 12AX7 giving two gain stages, one 1 MΩ volume control, a cathode-biased 6V6GT single-ended output, and a 5Y3GT rectifier — no tone control and no phase inverter, about five watts of the shortest signal path Fender ever shipped. Produced circa 1955–1957, it is the direct ancestor of the more familiar 5F1: same tube complement and nearly the same preamp, but with a choke-filtered power supply the 5F1 later dropped.

Circuit walkthrough (short form)

Two input jacks (each through its own 68 kΩ stopper, 1 MΩ grid leak) → V1A (12AX7, 100 kΩ plate load, 1.5 kΩ cathode bypassed by 25 µF) → 0.02 µF coupling → 1 MΩ volume pot → V1B (12AX7, 100 kΩ plate load, 1.5 kΩ cathode, left unbypassed so the feedback can work into it) → 0.02 µF coupling → V2 6V6GT (cathode-biased, 470 Ω 5 W with 25 µF bypass, 220 kΩ 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: 22 kΩ from the speaker jack into V1B's cathode — at DC this parallels the 1.5 kΩ cathode resistor through the secondary's near-zero DCR.

Power: a center-tapped HT winding feeds the 5Y3GT full-wave rectifier into a choke-filtered supply. The first 8 µF reservoir sits at +320 V; a filter choke drops it to +305 V, which supplies the 6V6 plate (through the output-transformer primary) and its screen; a 22 kΩ resistor then drops the rail to +260 V for the two 12 AX7 plates. Three 8 µF / 450 V cans do the filtering.

The choke, and what changed on the way to the 5F1

The 5E1's supply is the clearest fingerprint separating it from its descendant. Here a choke does the first bit of B+ filtering — reservoir +320 V down to +305 V — and the output tube runs its plate and screen off that single post-choke node. The 5F1 that followed replaced the choke with a plain 10 kΩ resistor, split the plate and screen onto separate rails, and shifted the reservoir up to +340 V. Same amp, quieter-on-paper filtering, one fewer iron part to buy.

Because the choke's DC resistance isn't printed anywhere on the drawing, the model estimates it from the chart itself: a +320 → +305 V drop carrying the roughly 43 mA the printed pin voltages imply works out to about 350 Ω, and the simulation settles on the same 42 mA self-consistently.

Verification

The drawing prints a full voltage chart (Fender's usual "read to ground with an electronic voltmeter, ±20%"), and the simulation matches every node on it: the 6V6 cathode within 0.1 % (+19.0 V vs +19 V), the output rail within 0.1 % (+305 V), and the preamp rail within 2.4 %. The rails are held to a tighter ±8 % internal verification target (the choke's DC resistance is estimated rather than printed, so the archive holds itself to a stricter bar there), while the two 12AX7 plates and cathodes are checked against Fender's printed ±20 % convention. The preamp stages simulate a little lean — plates near +178 V against the chart's +150 V — because the tube models are datasheet-typical while Fender measured production tubes of the day; the same gap shows up on every tweed circuit here. Planned refinements: the output transformer's primary resistance in the DC deck, and full curve-traced tube models.

Sources