I've spent some time in rec.audio.tubes to try and establish what this
is all about.

You could not have chosen a worse place - you will learn absolutely
nothing from that newsgroup. Read the Tube DIY forum on
www.audioasylum.com and you will find posts by the leading tube
designers. Try it out for a month or so. You will see a universe of
difference in the quality of engineering, debate, knowledge and
information. Plus it's leading edge - people experimenting with ideas.