Type RZ1-150 is a directly heated (4 V at 4 A) full wave rectifier and is rated at 1,000 V, 150 mA, which is no more than a type 5R4GY.
The exhibits we have of Type RZ1-150 all differ in height. This is the shortest at 140 mm and RZ1-150 is the tallest at 170 mm. The variation seems to be in the length of the pinch stem not the electrodes.
The serial number on this valve is 1297.
The anod front to back dimension is about 3 mm with a joining flange pointing in to the centre of the envelope.
The lower mica and filament. The filament is a tightly wound coil made into a wire. One piece forms the full M and so the middle lower support is s hook. RZ1-150 has ribbon filaments that are inverted V's with the middle point having a ribbon welded on wither side of the support. No oxide coating is visible and so it looks like a thoriated tungsten filament on this valve. On test at 4 Volts only one part of one filament heated up. No visible damage was seen but clearly this valve has issues.
The wide glass tube envelope is 51 mm in diameter and, excluding the L4 base pins, is 165 mm tall.
References: Private communication & 1043. Type RZ1-150 was first introduced in 1934.