The handful of sums that come up over and over on the bench — each one live, each one loaded with a real amplifier value to start from. Change a number and the answer updates as you type.
Enter any two of voltage, current, resistance, and power; the other two fill in.
Resistance accepts shorthand — 100k, 1M, 4k7.
Two resistors from a supply down to ground; the tap sits between them. R1 is the top (supply-side) resistor.
With the grid returned to ground, the cathode sits at the bias voltage. Give the target cathode current and that bias voltage to size the cathode resistor.
Each amp's parts list on this site records the cathode resistor that was actually fitted; this is the design target before tube spread and real-world tolerance. Browse the circuits to see the values in context.
A coupling capacitor and the following stage's grid-leak resistor form a high-pass filter. Below the corner, bass rolls away.
f₋₃dB = 1 / (2π · R · C). Cap accepts 0.02, 22n, 470p. Unsure what the "−3 dB" in that name means? See the units & notation guide.
Primary and secondary impedances set the turns ratio, and the turns ratio squared is the impedance ratio. Enter any two.