The NU13A is a later variant on the NU13 UK Navy rectifier and commercially would be the U15. The RZ1-250 has a higher maximum current rating.

The L4 base is 55 mm square.

The wide glass tube envelope is 48 mm in diameter and, excluding the L4 base pins, is 145 mm tall.

References: Datasheet & ¹⁰⁴³. Type NU13A was first introduced^¶ in 1934.

 
Pin Connections

L4	1	2	3	4
	a	f	f	-

 
Absolute Maximum Operating Conditions^¶

Rectifier	Vh	Ah	Va	mAa
	6.0	2.0	1,500	200

Thanks to Frank Philipse for supplying the above PDF datasheet