The 19H4 is a high voltage half wave rectifier, it is indirectly heated and uses a 2.5 Volt heater, the original American standard for AC heated valves.
The anode has a wide diameter central tube and four side flanges for greater surface area. The blackened outer surface of the anode aids radiation efficiency.
A closer view of the anode, ceramic support and top cap connection.
Thanks to Mark Mallison for sending the images.
The wide glass tube envelope is 40 mm in diameter, and excluding the IO base pins is 115 mm tall.
Reference: Data-sheet. Type 19H4 was first introduced in 1948. See also1948 adverts.