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.

21 thoughts on “Universal loadline calculator for vacuum tubes

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  1. Very useful calculators! Thanks for your hard work. Any chance of adding 6l6gc and perhaps 6v6 to the list?

  2. I appreciate your work here! Perhaps you should do a Patreon? I would certainly donate to this project. I use 6sl7 and 6sn7 quite a bit for preamp and phase inverter duty. Would love to 6v6 on here as well. Thank you!

      1. Great! Thanks! This is definitely going to in handy. Because the 6AK6 can be used as a power valve, could you also add it with a reactive load? Thanks in advance .

  3. How difficult would it be to implement parallel valves? Could it be as simple as maybe a tick box to double the current scale and push the load line down?

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