[Amps] Input Impedance of GI-7BT Triode

[K7ZS]

I have recently completed converting an MLA-2500B to use the GI-7BT Triodes.
Thanks to a lot of hand holding by Lawson, W4EMF!

Now, I am building WD7S's great little TU-7B tuned input board to allow
driving the amp with a modern tranceiver which does not have an auto-tuner.

I am wondering how to determine the input impedance of these tubes.  Plate
voltage is around 2300v.  I have the data sheet, but am not seeing any
reference to the input impedance since this is a tube designed for pulsed
microwave service.

Any help would be much appreciated!

73 Kevin K7ZS
Portland, Oregon
k7zs at earthlink.net