The 304T is a 300 watt triode with a mu of 12 made by paralleling four 75T tubes in one envelope. This tube was the ancestor of the 304TL/TH series. It is similar to the later 304TL tube except for the lowered and inverted internal shield. The inverted shield is known to have been raised higher in later varieties. In the second example a single pin emerges from the envelope similar to late 304TL tubes. The 304T marking on the glass may only mean Eimac was using older glass for the experiment and the tube dates after the TL tubes were in production. The grid pin is spot welded in 4 places to the shield. The last example may be the oldest version as it doesn't have the internal shield.
Length = 7.63" Diameter = 3.56"
Max voltage = 3000
Max current = 900 ma
Fil voltage = 5 or 10
Fil current = 25 or 12.5 amps