The 70L7GT is an american valve designed for equipment without an isolating mains transformer. The 150 mA heater is designed for heater chain service. This valve is unusual in that in addition to a 1.8 W audio output pentode the envelope also contains a half wave rectifier as well.
The rectifier needs a minimum series resistance of 15 Ω. The audio output at 1.8 W is at 10% distortion.
The Raytheon logo on the base. For details of the electrodes See 70L7GT.
The top of the envelope. The rectifier heater has eight loops visible making 16 heating strands all in series. Above the top mica can be seen the cooling fins for both control grid and screen.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 69 mm tall.
References: data-sheet. Type 70L7GT was first introduced in 1947.