The DL33 (3Q5GT) is a dry battery audio output pentode. The directly heated filament is only rated for DC use. Even at 2.8 Volts, with the centre tap grounded, the AC hum would be impossible to live with.
This is an imported valve with the term Foreign added to the glass to point out that this was not a British product.
The elliptical anode from the end. At the right can be seen the etched octagon that contains the Type designation 3Q5GT - an American made valve rebranded by Pinnacle.
The top mica. The filament tensioning springs can be seen as fine wires. The filament is kept straight as it passes through the grids by being held in a diamond shaped hole in the top mica with the springs pulling away at an angle.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 61 mm tall.
References: Data-sheet, 1040, 1043 & 3002. Type DL33 was first introduced in 1946. See also1946 adverts.
