Had a contact with Stephen, VK2BLQ, who reports that I sound normal so that's all good. Plate and Load knobs are new to me but fun to learn about.
For my younger readers, this is what a valve looks like:
The compass was fascinating, it uses a spinning coil with an amplifier in the centre. Power is fed in through the ball bearings and the output is sent by an LED light.
We turned it on and compared with a compass in a smartphone.
A wonderful device, but I think technology may have moved on.