The EL3 is an audio output pentode from 1938. Ten years later the uprated version was the EL3N that was functionally equivalent to the EL33 that was fitted with a standard IO base cap.
The anode is oval in shape. The control grid is fitted with radiating fins at the top of the supports. The suppressor grid supports extend up to a secondary mica sheet that fits tight in the top of the envelope and holds the electrodes firm.
A closer view of the upper part of the anode and inner components. The cathode tube is oval but a slightly different profile to the anode. The g3 pitch is very wide.
The classic envelope is 43 mm in diameter and, including the Ct8 base pins is 114 mm tall.
References: Data-sheet, 1040 & 1043. Type EL3 was first introduced in 1938.