KT88 mutual characteristics?

[diynewb83]

As part of my search for knowledge, I've also supplemented with Merlin's Valve Wizard site, specifically this page: The Valve Wizard -Single Ended

As part of calculating screen characteristics, he has mentioned the mutual characteristics graph from a particular valve. I've searched around a bit on KT88, and I've seen regular plate characteristic graphs for different screen voltages, but not quite illustrated this way, and he hasn't gone into any detail as to how to interpret this if you don't have the proper graphs.

Does anyone have these graphs for the KT88, or can point me to some reading for how to figure it out in a different fashion?

 

[fiatguy85]

LTSpice will give you pretty much any curve you can figure out a way to plot:

LTSpice Howto

Tube Spice Models

 

[PCL200]

You can construct a "mutual conductance graph" for the KT88 using the Ia/Va graphs in the datasheets for the KT88.

In this datasheet there are Ia/Va graphs for four different values of Vg2 (100, 150, 200 and 300 V). You can combine these four different values for Vg2 with about any Va you wish.

Let's say you want the mutual conductance graph for Va = 400 V and Vg2 = 300 V. From the Ia/Va graph for Vg2 = 300 V you can see that at Va = 400 V:

Ia = 292 mA at Vg1 = - 10 V
Ia = 214 mA at Vg1 = - 15 V
Ia = 162 mA at Vg1 = - 20 V
Ia = 122 mA at Vg1 = - 25 V
and so on

Now you have the input to draw a "mutual conductance graph" (or Ia/Vg graph) for a KT88 at Va = 400 V and Vg2 = 300 V.

 

[diynewb83]

Thanks folks! This is exactly what I was trying to learn.