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The 4033A is an interesting valve with the electrodes inclined at 45 degrees and it was used in telephone repeaters. It was the professional version of the PA1. The valve was introduced in the mid 1930s but was difficult to mass produce and was black-listed from use in military or essential commercial equipment in WWII.

The complexity of the design can be seen better in CV1220.

The 4033A has an anode dissipation of 25 Watts and can be used to 10 MHZ with reduce ratings. As an audio valve in single end configuration with a 7,000 Ω load and 400 Volts on the anode it will generate 4 Watts with low distortion.

The balloon envelope is 52 mm in diameter and, excluding the B5 base pins, is 103 mm tall.

References: Data-sheet & private communication.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.