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These two early French triodes, probably made by Société La Radiotechnique and branded 'Radio Micro', while almost identical in external appearance are quite different. The first has a classic horizontal tubular 'R' type anode and with a cold filament resistance of 1 ohm, was probably a bright emitter. The second has a horizontal oval box anode and, with a cold filament resistance of 2.5 ohms was probably a dull emitter. Neither valve has any detectable markings.
The picture below shows one of these valves with an earlier 'RadioMicro' metal based triode and a later 'Spécial' from the same Société La Radiotechnique company. Notice the close similarity of the bases of the last two.
This page last modified by AJC on Friday, 26-Mar-2010