In 2019 the old WW1 RAF Syntoniser shown below, came into my possession. It was made by Siemens Brother & Co. Ltd of London. I’ve never seen another one and can’t find out much about it on the web. I think these came into use at the end of WW1 and were used by the RAF up until newer designs took over, nearer WW2. The calibration date on this one is 21st September 1928.
Each one was calibrated using a designated and numbered valve, in this case number 1839. The later R502 wavemeter was also calibrated with a specific, numbered valve. The R502 and later BC-221 each had calibration charts, without which they were not of much use.
The Syntoniser uses a single supply of just 6v and this one actually works.
Professor Anthony C Davies made a presentation at Oxford University on WW1 wavemeters. You can find his handout here. Note that if that link ever stops working, let me know and I’ll share it directly.
Rather than have a page full of pictures, I’ve created a slider carousel of pictures which you will find below. Warning: I hold the Copyright on all these images and you may not share them without permission.