The 4-65A or 8165 is a 65 watt dissipation tetrode. The usable frequency for maximum ratings is 150 MHz. The first example is an early (1947) version with individual uranimum base seals. The second example is version made for the Navy with a flat uranium glass base. The third example may have been an experiment as it is marked with the PPG glass logo. It wasn't company policy to allow suppliers markings on their tubes. The fourth example is a late production Eimac tube and the fifth example was made by Penta (PL-8165/4-65A). The sixth example was made by RCA.
Length = 4.38" Diameter = 2.38"
Max voltage = 3000
Max current = 150 ma
Fil voltage = 6
Fil current = 3.5 amps