This Mazda second-generation double-diode-pentode was (we think) redesigned as a double-diode beam tetrode during the latter part of its production life. The picture shows a valve of relatively late manufacture.
The PenDD4020 had rather better gain than the Pen453DD and was correspondingly more successful, being used in a good number of AC/DC Murphy sets from around 1936 onwards. A good valve but, interestingly, its eventual end of life was often due to failure of the diode cathode emission rather than weakness in the pentode section.
The classic envelope is 51 mm in diameter and, excluding the B7 base pins, is 124 mm tall.
References: Datasheet & 1043. Type PenDD4020 was first introduced in 1935.
Absolute Maximum Operating Conditions¶
Updated August 29, 2018. shape:classic construction:pinch type:double.diode.pentode age:1930.1940 base:b7 heater:200ma pins:7 pin:1.a(d1) pin:2.a pin:3.a(d2) pin:4.h pin:5.h pin:6.k pin:7.g2 pin:tc.g1