The 75 is a double diode triode for superhet AM detection, AGC detection and first audio voltage amplifier.
The 75 has a 6.3 Volt heater and a UX6 base. The 2A6 has the same rating and base but a 2.5 Volt heater. The 6B6G is also the same basic valve but has an IO base.
Slightly enhanced to show the Made in US in the circle on the envelope. The base cap carries the Raytheon name.
The Raytheon brand label.
The diode anodes are within the bright box below the triode. The triode control grid is visible above the mica disc. The anode is stitched together with the metal being splayed out around the hole.
The classic envelope is 38 mm in diameter, and excluding the UX6 base pins is 98 mm tall.
Reference: Data-sheet. Type 75 was first introduced in 1937. See also1937 adverts.
