Just got two of these in for the collection ...
Base: UX-Base (4 Pins (2 thick, USA 1924, UX) 2 Top contacts.
Filament: Vf 5 Volts / If 3 Ampere / Direct / Specified voltage AND current AC/DC
Description: High-rel, high altitude (60000ft) version of 1641, full wave rectifier. 2.3KV PIV, 275mA average current. Designed and manufactured by United Electronics. The reference to RCA as developer is wrong.
Base: UX-Base (4 Pins (2 thick, USA 1924, UX) 2 Top contacts.
Filament: Vf 5 Volts / If 3 Ampere / Direct / Specified voltage AND current AC/DC
Description: High-rel, high altitude (60000ft) version of 1641, full wave rectifier. 2.3KV PIV, 275mA average current. Designed and manufactured by United Electronics. The reference to RCA as developer is wrong.