Managed to get a pair of 24a for THD testing. A great driver used in 45 SE DC-coupled design. 
24a tetrode curves
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Hi Ale. Thanks for the curves. I want to see THD. In particular, the output level of ~ 100 volts for use with lamp 6S4S. Thank you.
Svetlana.
Hi Svetlana. Unfortunately one of the valves I got looks like has some intermittent failure. Not sure if it’s the socket.
I will have to build a screen regulator as don’t have a second power supply for this. The screen regulator will be fed from the anode. Probably a simple resistor divider (e.g. potentiometer) and a source follower.
Are you looking to run this valve with screen at +90V?
For 100Vpp and some additional headroom, I will be looking at biasing this at 250V anode voltage at least, what do you think?
Ale
Hi Ale. I badly translated what you wrote.I’ll try to write this .I want to see not only the THD 22.22dBu ( 10 Vrms) and 31.249dBu (28.284Vrms).
Svetlana