regular values of gm for a small-signal vacuum tube are one to ten millisiemens. It has become the three 'constants' of the vacuum tube, one other two becoming its gain μ and plate resistance Rp or Ra. The Van der Bijl https://blog.globalgoodsguru.com/exploring-the-superiority-of-silicon-carbide-tubes-in-industrial-applications-fe95cea9bf5d