Sensibly equivalent¶ to:
The WD709 is a variable μ amplifier pentode and a pair of signal diodes in the one envelope. Probably this was designed as was the later EBF89 as final IF amplifier and AM detector. The other diode would provide AGC rectification.
WD709 is an M-OV Type designation but this exhibit carries no makers name.
Most of the electrodes are hidden, the only clear components are the insulated heater and cathode tube in the centre.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 59 mm tall.
References: Data-sheet & 1040. Type WD709 was first introduced in 1950.
Absolute Maximum Operating Conditions¶
Updated September 12, 2013. shape:thin.glass.tube construction:all.glass type:double.diode.pentode age:1950.1960 base:b9a heater:6.3v pins:9 pin:1.g2 pin:2.g1 pin:3.k.s pin:4.h pin:5.h pin:6.a pin:7.a(d1) pin:8.a(d2) pin:9.g3