Sensibly equivalent¶ to:
The KT21 was a battery output valve but not a beam tetrode valve. It was a modified version of the KT2 designed to be extremely economical in respect of anode current consumption and was intended to be used in sets which did not have a separate grid bias battery. The user penalty for these improvements was an extra 0.1A of filament current. It was designed for maximum amplification.
The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 100 mm tall.
References: Data-sheet, 1040 & 1043. Type KT21 was first introduced in 1937. See also 1937 adverts.
Absolute Maximum Operating Conditions¶
Updated January 13, 2013.