The 75C1 is a high stability voltage stabiliser. The output voltage is 75 Volts and for currents of 2 - 60 mA the regulation is between 5 and 8 volts.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 45 mm tall.
References: Data-sheet & 1040. Type 75C1 was first introduced in 1957.