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The BTH B11 dates from 1927 and was designed for audio output. It has an amplification factor of 3.5.

This valve was not clearly marked with a type designation. As the single strand inverted V thoriated filament was intact the valve filament was heated to check its rating. The filament was slowly energised by a constant current source to minimise thermal shock. At each current setting the voltage across the filament was noted. Armed with a list of filament requirements for the BTH valves of the period, the current was increased until a match was obtained. This exhibit took 0.6A at 6.0 volts and the filament glowed an orange/yellow.

The construction of the electrodes is made rigid with stout support rods.

The balloon envelope is 43 mm in diameter, and excluding the B4 base pins is 97 mm tall.

Reference: ¹⁰⁴³. Type B11 was first introduced in 1927. See also 1927 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶