The 0B2 is a B7G voltage stabilizer. These devices were made obsolete by the Zener diode.

The regulation of the 0B2 was 3.5 Volts for currents of between 5 and 30 mA. So the voltage across this tube in service would have been held at between 106 and 110 volts. The tube strikes at a voltage of 133 volts.

The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 57 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type 0B2 was first introduced^¶ in 1948.

 
Pin Connections

B7G	1	2	3	4	5	6	7
	a	k	ic	k	a	ic	k

 
Absolute Maximum Operating Conditions^¶

Stabiliser	Va	mAa
	108	30

Thanks to Frank Philipse for supplying the above PDF datasheet