The 250TH or VT-220 replaced the 250T "HI" version in the late 1930s. This is a 250 watt triode with a mu of 37. After WWII, the plate material was replaced. They are usable up to 40 MHz at full rating. When first announced, the maximum plate voltage was 3000 and the amplification factor was 32. The third example was made by General Electronics, the fourth by ICE, the fifth by Lewis and Kaufman, the sixth by Jennings, the seventh by Heintz & Kaufman and the eighth by Sylvania.
Length = 10.13" Diameter = 3.81"
Max voltage = 4000
Max current = 350 ma
Fil voltage = 5
Fil current = 10.5 amps