You don't really need a valve tester.
A HT supply for the anode. Bench PSU for the heater. Another bench PSU with a pot across its output for the grid.
Heat it up, change the grid voltage by 1V and measure the anode current change, gm.
Heat it up, apply a megger across the other electrodes to measure any leakage.
Done, just about.
The tricky one is the HT supply if you don't have a suitable transformer, but a couple of 60V bench PSUs in series will just about do, and useful for lots of other things.