It's an early 1920s valve. Valves like this were used in the very first broadcast receivers around the time the BBC was formed. This one still works, which given its age and type is probably unusual - it's a bright emitter or "r-type" so only has a few hundred hours working life. With the heater connected to a 1.5V cell it lights up like a light bulb! You can just about make out the internal construction in the photo - a thin wire filament (cathode) with a spiral grid inside a cylinder (anode).Since there's not a lot on information on very old valves on the web here's some technical details. Manufacturer: Métal Radio (France). Model: BW 303. Markings: 1,6 - 1,8V 30 - 75V XX.
Now I must go and try and fix my AVO valve tester, it's cutting out and putting 110V across the heater terminals. Perhaps this has something to do with the 0V and 110V coarse setting for heater voltage being next to each other....
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It's fixed. For now at least. The wiring to the switches is still the original lacquered cotton stuff and in places the wire has cut through, presumably a very small amount of friction over many years. Anyway, pushing the bundle of wires by the heater voltage switch away from the switches fixed the problem. Then I managed to send the meter to full deflection and it stuck - so I had to open that up by removing the 2BA nuts on its terminals and pulling the whole movement through the front panel. Not the first time I've had to do this, there are a few bits of rust on the magnet and they can cause it to jam. Hopefully this problem will go away if I make more frequent use of the instrument.
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