Universal loadline calculator for vacuum tubes

This calculator allows you to trace the anode characteristics graph, and to compute and tune loadline and operating point of various vacuum tubes.

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, pentode, and triode mode,
  • set Single-Ended or Push-Pull configuration
  • set the Power Supply V+ voltage, the screen voltage, the screen tap, the quiescent bias current.
  • set the output headroom

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
Select a Tube:
Operating mode:
V+ (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):

If you are not familiar with loadlines, their purpose, and their use, I suggest you checking my guide: Section 3.2 (for resistive loadlines), Section 4.1.3 (for reactive loadlines), and Section 4.2.2 (for AC loadlines).

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

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