A pair of signal diodes are to be found in the DD620, A Mazda valve from 1934, intended for use in universal mains sets (transformerless for AC or DC use). For this application the heater cathode insulation has been designed to withstand a high voltage difference.
The envelope on this exhibit is some 9 mm taller than our other DD620.
The large canopy or screen seen end on. The two anodes are within.
The dome carries all of the available information.
The lower anode is visible. The top anode is the same but rotated through 180 degrees and fixed to the left support.
The balloon envelope is 41 mm in diameter and, excluding the B5 base pins, is 82 mm tall.
References: Datasheet & 1040. Type DD620 was first introduced in 1934.