Universal Loadline calculator for vacuum tubes

This calculator allows you to compute and tune loadline and operating point of various vacuum tubes.

Select a Tube:
Operating mode:
B+ (V): Grid Bias Voltage (V):
Quiescent Operating Point: Iq(mA):
Max Output Power (W):
Load (Ohm): HD%:
Next stage AC Impedance (Ohm):
Screen Voltage (V):
UltraLinear tap (%):
Out. headroom (+/-V):

It considers both reactive loads (for vacuum tubes used in output power stages) and resistive load (for the other stages).

You can:

  • choose among most common vacuum tubes (I am slowly adding more),
  • set the operation modality, among ultralinear (for power tubes with reactive load), pentode, and triode mode,
  • set Single-Ended or Push-Pull configuration
  • set the B+ voltage, the screen voltage, the screen tap, the quiescent bias current.
  • set the needed output headroom, for pre/phase-split tubes

The calculator:

  • plots the anode characteristic graph, for the chosen operation modality,
  • plots the reactive loadline for reactive load,
  • plots the DC and AC loadlines for resistive load,
  • highlights the operating point,
  • highlights the needed output headroom, if set,
  • estimates the grid bias voltage,
  • estimates the maximum expected power, across the load.
  • estimates the Harmonic Distortion (HD) in the operating range corresponding to the selected output headroom

The underlying model and equations, for tracing anode characteristics curves, are those discussed by Norman Koren, in his web site.

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