A schematic is a map of the circuit, not a picture of the chassis. Every part is a symbol and every line a connection — and once you know the handful of symbols a tube amp uses, the drawings in this archive read straight through, from the input jack on the left to the speaker on the right. This is that handful, drawn the way the archive draws them.
Signal flows left to right. The input jack sits at the left edge, each amplifying stage a little further right, and the output transformer and speaker at the far right. To follow the sound, read across the page in that direction.
Power lives apart, along the top and bottom. The high-voltage supply runs as labelled rails (B+1, B+2, B+3) rather than one long wire; ground — the common 0 V return — sits at the bottom. A part connects up to a rail or down to ground by name, so the drawing never becomes a web of crossing lines.
One tube is one stage. Each triode or output tube, together with its plate resistor, its cathode parts, and the capacitor that couples it to the next tube, is a self-contained gain stage. Count the tubes and you have counted the stages.
These are the exact shapes used in this archive’s schematics, redrawn from its KiCad symbol library. Every circuit page is built from them, so a symbol learned here appears unchanged on every amplifier. Colour marks the electrodes of each tube — plate amber, control grid green, screen grid gold, cathode teal — the same coding as the pinout diagrams.
To keep a drawing legible, the supply and ground connections are written as labels instead of wires. A tag reading B+1 is a named wire; the same tag anywhere else on the sheet is the same wire, joined without a line drawn between them. That is why a plate resistor can rise to B+ and a cathode resistor drop to ground with only a short stub and a name.
Supply rails carry the plate voltage — hundreds of volts — and enter a stage from above; several appear because the voltage is dropped and cleaned in steps (B+1 is the highest, B+3 the lowest and quietest). Ground is the 0 V return everything measures against and is drawn at the bottom. This archive marks ground with a GND label rather than the three-line ground symbol above, but they name the same node.
Here is a single gain stage — the pattern that repeats through every preamp. The signal arrives at the grid on the left and leaves, amplified, from the plate on the right. Hover, tap, or focus each part to read its job.
Hover, tap, or focus a part of the stage to read what it does.
Read left to right, that is the whole story of a preamp stage: the coupling capacitor lets the previous stage’s audio onto the grid but not its DC; the grid-leak resistor holds the grid at ground for a bias reference; the cathode resistor sets how hard the tube runs and its bypass capacitor keeps that setting from eating the gain; the tube amplifies; and the plate-load resistor converts the result into the output voltage, which the next coupling capacitor passes along. Every triode stage in the archive is a variation on exactly this.
The capacitor between one plate and the next grid does two things at once. It blocks DC — the plate sits at a couple of hundred volts, the next grid near zero, and the cap keeps those apart — while it passes AC, the audio riding on top. Paired with the grid-leak resistor it also forms a high-pass filter, so its value sets how much low end survives the hop: a 0.1 µF · 400 V cap into 1 MΩ passes everything, a small 0.001 µF cap deliberately thins the bass. Put numbers to that corner with the coupling-cap tool in the calculators.
The other half of the drawing is the power supply, and it has its own left-to-right flow. The rectifier turns the transformer’s AC into DC; a reservoir capacitor smooths it; then a chain of dropping resistors and more capacitors steps the voltage down and cleans it, handing out a rail at each node.
Follow it across: the high-voltage winding (HT) meets the rectifier, whose output charges the first 16 µF capacitor to make B+1 — the stiffest, highest rail, feeding the output tubes. Each resistor after it drops a little voltage, and each capacitor shunts the leftover ripple to ground, so B+2 (the screens) and B+3 (the preamp) come out progressively lower and quieter. A stage taps whichever rail suits it — the preamp wants the cleanest, so its plate loads climb to B+3. Every part here is a symbol already met above: a tube rectifier, capacitors, and resistors.
Put it together on a real drawing. The first stage of the 5E3 is a textbook example of the pattern above — here is how it reads, part by part, straight off the schematic.
The instrument jack feeds a 68 kΩ grid stopper into the grid of V1A, one half of the 12AY7 twin triode. A 1 MΩ grid-leak resistor holds that grid at ground. From the cathode, a single 820 Ω resistor — shared with the other channel’s triode and bypassed by a 25 µF · 25 V capacitor — sets the bias. The plate climbs through a 100 kΩ load resistor to the B+3 preamp rail, where the archive’s published measurements put it near 140 V. And a 0.1 µF · 400 V coupling capacitor carries the amplified signal off the plate to the 1 MΩ volume control and the stage that follows.
That is the same six ideas — coupling in, grid leak, cathode RC, the tube, plate load, coupling out — with this circuit’s actual values filled in. Open the 5E3’s interactive schematic and the whole amplifier is this stage and its siblings, chained left to right into the 6V6 output pair and the 8 kΩ : 8 Ω output transformer, with the 5Y3 power supply along the bottom.
Every symbol on this page is original artwork, redrawn from this archive’s KiCad symbol library (pipeline/schematic_lib.py); the 5E3 values and the ~140 V first-stage plate figure are read from the published Fender 5E3 (F-EE) drawing and Rob Robinette’s published 5E3 measurements, as recorded on the 5E3 circuit page.