The 0B2 is one of the B7G voltage stabilizer that were the last to be developed in the 1950's before semiconductors took over.

The regulation of this tube 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 striking voltage was 133 volts.

The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 45 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type OB2 was first introduced^¶ in 1957.

 
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