The 42 is an audio output pentode, with a low output rating, but when used in push pull a pair could deliver 18.5 Watts in class AB2.
Also on a UX6 base is the 2.5 Volt 2A5 that is electrically equal to the type 42. The Type 6F6 is also electrically identical, but on an IO base.
The anode is cylindrical with side fins. The control grid is wound on copper supports with heat sinks on top. The mica supports fit tightly against the glass to prevent movement.
The anode face view. The suppressor grid can be seen in the space between the anode and the top mica.
The classic envelope is 45 mm in diameter and, excluding the UX6 base pins, is 102 mm tall.
References: Data-sheet, 1040 & 1043. Type 42 was first introduced in 1936. See also1936 adverts.
