The TH233 is a triode heptode frequency changer for 200 mA series heater chains. The TH2321 is the same basic design but with higher internal capacitances and the older B7 base.
This exhibit is unused and came in the original box surrounded by corrugated card and wrapped in protective paper.
The reverse is plain zinc paint.
The classic envelope is 32 mm in diameter, and excluding the MO base pins is 89 mm tall.
References: Data-sheet, 1040 & 1043. Type TH233 was first introduced in 1939. See also 1939 adverts.
Absolute Maximum Operating Conditions¶
Updated November 04, 2020.