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The Round Type N is a "soft" triode, actually the second early triode in the UK after the Round type C. Type N has an asbestos pellet in a 10 mm tube above the envelope. Quite different to the von Lieben Triode is also the grid, but similar to early Papaleksi tubes. Both, Lieben and Papaleksi use an apendix, but not for Asbestus, but Quicksilver Amalgam. The Round Type N triode was first used in the Marconi Receiver Type 27 from 1914 (or 1915) to 1918.
------------------------ Giorgio Basile:
MARCONIS W.T. Co. Ltd. Type N (2V-PIF) Round Valve
Triode
Serial Number: N9217. Ca. 1915.
“2V-PIF” stands for: Heater 2V • Platinum Iridium Filament.
The first work in triode valve development in Great Britain seems to have been done about 1911 by Captain H. J. Round of the British Marconi Company. The Round valves were first employed by Round as high-frequency amplifiers, later as oscillators. They were remarkably good amplifiers when operated under optimum conditions.
The essential features of the Round valves are:
• the cathode is of the Wehnelt, or oxide-coated, type;
• the grid is a fine mesh surrounding the filament;
• the anode is a cylinder surrounding the grid;
• there is a tubulation containing a wad of asbestos extending upward from the top of the bulb.
The Type N has a single lime-coated filament which operates with a current of 2.5 A, 40-80 V on the anode, and was used in the famous Marconi No. 16 circuit, which had a carborundum detector. The valve functioned in this circuit as a radio-frequency and audio-frequency amplifier, the circuit being of the reflex type.
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