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Triotron universal-type indirectly heated valves, showing the P2020N and the S2034N.
In the Triotron range of valves is a series of indirectly heated types/fitted with 20 Volt filaments and taking 0.18 A each which have been designed for use either on AC or DC supplies, the customary arrangement being to join their heaters in series and drop the surplus volts in a resistance. These are suitable for use in universal-type sets, and the series includes two screened HF pentodes - one a variable-μ type - a triode, and an output pentode. There is also a half-wave HT rectifier with a 30 Volt filament taking 0.18 A for use in conjunction with these valves on AC supplies. It gives 70 mA DC output.
A specimen variable-μ pentode, type S2034N, was tested with 200 Volts on the anode, 100 Volts on the screen, and at zero grid bias had a mutual conductance of 2.7 mA/Volt. The amplification was 1,900, It passed 5.8 mA in the anode circuit and 2.6 mA in the screen circuit. The valve is metallised and fitted with a five-pin base with the anode terminal at the top of the bulb. A grid bias of 7.5 Volts changed the conductance to 0.05 mA/V, while the amplification fell to 900.
The S2035N HF pentode was also tested and quite satisfactory results obtained. It has a five-pin base and a metallised bulb. With the P2020N output pentode a mutual conductance of 1.5 mA/Volt was obtained under working conditions, that is to say, with 200 Volts on the anode and on the auxiliary grid, and with -18 Volts grid bias. It passed 21.5 mA anode current and 8.4 mA in the auxiliary grid circuit, making a total of 29.6 mA in all. It is rated to give 1,350 milliWatts output when working into a 10,000 Ω load.
The price of each of these three valves is 12s. 6d.e, and the suppliers are Triotron Radio Co., Ltd., Triotron.House, Bloomsbury Street, London, WC1.
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