The PM4DX is a medium impedance triode for use as a detector. Exhibit PM4DX has the identification etched into the glass, this exhibit carries a paper band on the Bakelite base and has details printed on the dome of the envelope.![](../pics/aal0015a.jpg)
The balloon envelope is 43 mm in diameter, and excluding the B4 base pins, is 87 mm tall.References: 1931 data-sheet & 1043. Type PM4DX was first introduced in 1928. See also 1928 adverts. |