usual values of gm for a small-sign vacuum tube are 1 to 10 millisiemens. It is probably the 3 'constants' of the vacuum tube, another two remaining its gain μ and plate resistance Rp or Ra. The Van der Bijl equation https://sairaiisc957711.onzeblog.com/30726852/5-essential-elements-for-edgetech-industries-eti