From Eham Forum… Post by: WF0H on February 23, 2003… I am not sure when this started, but it was well established in the early 1950’s, which were probably the heyday of the 807 tube. I once had a Johnson-Viking mobile rig from the late 1940’s that had an 807 final in it – a wonderful CW and AM rig, too. In the 1930s, the popular tube was the Model 45. By the late 1950’s, the tube of choice was the 6146, so it probably stared someplace in between those two eras.