The HP211 and HP211C from Tungsram are vari-μ RF pentodes that operate from battery supplies. We can not, as yet, find out what made the 1937 HP211C different from the 1934 original. Both were made with B4 or B7 base caps.
This exhibit has an unusually long base cap. In fact it is a B4 base that has been wired to the lower B7 base cap.
The pinch is clearly visible but the grids are partly obscured by the gettering.
With a little enhancement the grid wires can be seen more clearly.
More enhancement. The identification lettering on the glass can be seen. The initial H is missing.
The classic envelope is 44 mm in diameter, and excluding the B7 base pins is 130 mm tall.
Reference: 1043. Type HP211C was first introduced in 1937. See also1937 adverts.
