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 and resistive load.

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 load type as reactive or resistive
  • 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 expected power at the load when max Grid Voltage is the maximum displayed, when max Grid Voltage is 0, when operating in Class A or A2, and at the selected output voltage headroom.
  • estimates the Harmonic Distortion (HD) in the operating range corresponding to the selected output headroom

Did you buy my book? Remember to leave a review on amazon!

Select a Tube:
Operating mode:
V+ (V): Grid Bias Voltage (V):
Quiescent Operating Point: Iq(mA):
Output Power (W):

Load (Ohm):

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.

96 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?

  4. Hi Giuseppe, I don’t know if it’s easy to do but having some double triodes on reactive loads would be a hell of and add-on ! I’m thinking 6SN7 push pull, 12AU7 push pull… Maybe it is possible since you have the models? That would be nice!
    Your simulator is so much quicker than opening Orcad or another spice simulator.
    Thanks for the amazing work !

  5. Thanks Giuseppe for this amazing calculator. I was just checking it against a 2A3 data sheet and they match beautifully. Any chance of adding the JJ 2A3..?

  6. Great job! My congratulations! I would also like to see EL86, 6AH6 and other, less common tubes, such as A2134.

    Best regards!

  7. Hello Giuseppe, greetings from Greece

    This online curve calculator is a really nice work, congrats!
    Can you please add GM70 & GU50 to your list with positive grid curves

    Keep going with all good fortune


  8. Dear all,
    thanks for using this calculator and thanks for suggesting additional tubes.
    The pending list of tubes that will be added now includes:

    ECL84, ECL85
    EL86, 6AH6, A2134, 12E1
    GM70, GU50
    6GU7 6CG7 12BH7
    45, 101D, 205D

    Hope to be able to add them all in a couple of weeks.

  9. Very nice tool Giuseppe!!! When I compare tubes it seems for example EL34 use 0V as Control Grid voltage when this calculates Power so Anode Current comes lower and Anode Voltage higher than for example 6L6GC which use +15V Controd Grid voltage. I just bought your Kindle book which I hope explains how it is possible to use CG positive values…

  10. Sorry Giuseppe! Now the previous comments did open for me to read and you have already pointed to chapter where it is explained.

          1. Thanks I seen.
            6N7/6N7P/6H7C are Same Tube ,6N7 is US Model,6N7P is China Model,6H7C is Soviet Model. It’s use for the low power Class-B PP.

  11. Hello, Giuseppe! If possible, please add E180F and EL803S. I will be very grateful!

  12. Buongiorno Giuseppe, complimenti per il tuo lavoro!!! Potresti aggiungere la 845? per la 211 e 845 sarebbe interessante qualche valore di griglia positiva!

    1. Tra l’altro, considera che per la 211 ci sono già le curve con valori positivi di griglia.
      By The way, note that 211 already has positive grid values available.

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