The 1AB5 is a battery RF pentode with a higher μ than Type 1LN5. Use would be as RF amplifier or mixer. This exhibit has a slightly different construction to our other 1AB5 from Sylvania.
The very small pentode section is mounted horizontally and low to the base and pins.
The anode held between end mica sheets. The whole assembly is then held by a top mica sheet above the pentode section. Through gaps in the anode the control grid can be seen. The filament is a single wire.
The gettering is inside the dome, the outside of which carries the Type designation.
The wide glass tube envelope is 29 mm in diameter, and excluding the B8B base pins is 44 mm tall.
References: Datasheet. Type 1AB5 was first introduced in 1949.