Together they presented on the theory and practice of constructing using valve technology.
John handed around common valves including a tiny device and told the story of his first home made valve radio. The theory of how valves work, by using heat to emit electrons and then using charged grids to control their flow in the vacuum chamber is at once, both simple and sophisticated.
Stephen talked about where to pick up common valves even today and showed some of his past projects which are beautifully constructed.
The board he's holding here is a regenerative receiver that is powered by batteries including just 9V for the plate voltage.
It was pointed out the the electromagnetic pulse from a nuclear explosion (or even a devices specifically designed to generate an EMP) will kill most modern technology and if we want to have a chance to participate in the post apocalyptic radio skeds we'd better get on and build some valve equipment.
Luckily, the group that turned up managed to fit into the air-conditioned WIA hut today, but it's great news that the construction of a larger shed on the Dural block is finally going ahead.
I can still remember valve equipment (aside from that big tube at the front of televisions until recently), but my children have no idea about this technology.
It won't be long until all living memory is gone.