The PM3A was introduced in 1927 as a resistance capacity coupled amplifier triode with a μ of 35.
The identification details are etched onto the side of the envelope together with a code 7C68. The main details are also carried on a paper strip fixed above the Bakelite base. Looking up under the mirror of the Magnesium gettering reveals a horizontal box anode. This is supported from the pinch by stout wires that form a wide U. The anode is stippled.
The Balloon envelope is 43 mm in diameter, and excluding the B4 base pins, is 90 mm tall.
References: 1931 data-sheet & 1043. Type PM3A was first introduced in 1927.
Absolute Maximum Operating Conditions¶
Thanks to Andy Cowley for supplying the above PDF datasheet.
Updated December21, 2012. shape:balloon construction:pinch type:triode age:1920.1930 base:b4 heater:4.0v pins:4 pin: