Pa = 75W
This gridless GAMMATRON was developed so as not to infringe with the Lee de Forest patent (owner RCA) on the control grid. Instead, the plate close to the filament has influence on the electron flow towards the other plate (anode). Base is a stepped "giant" 4 pin type. The tube originally had a graphite anode. The grids was changed to a tantalum "Gamma Plate" which was operated with a negative bias. The tube was uused in class A and B audio amolifier circuits as well as class B RF amplifiers. .
We are not sure if the other early Gammatrons like HK155 and HK255 were ever produced but certain on this HK55 since one is in the Al Jones Collection.
