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 side view shows the HT rectifier on the left and the audio section on the right.
This view is looking into the rectifier anode. The pentode anode is wider and can be seen behind the rectifier. Both are carbonised to radiate heat more efficiently.
A close-up of the base of the rectifier.
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. See also1947 adverts.
