Heath-Robinson-Style One Valve Receiver

[Sparks]

Thanks, that makes things a lot clearer. Sounds just like an adaptation of a tuning slug, or maybe an early version of it. I once came across a short-wave transmitter where the tuning of the final stage was done by pushing a brass rod in or out of the front panel, it moved a great lump of metal in and out of the large coil. Probably easy enough to make, but I wonder how good (or bad) they were?
Bob