Actually, I think Drake was pretty clever. The tubes cost roughly half as
much as a 6146 and had about the same capabilities. Drake was smart enough
to run them within their ratings, unlike most other manufacturers that used
horizontal output tubes and tried to sqeeze every last watt out of them.
Add to that the fact that (according to tests results in the Bill Orr
Handbook) they actually had less distortion than the 6146 in linear
service, and it looks like a darn good decision.

I still remember a friend of mine running his TR4 full bore on 20 meters
RTTY back in the 1970's. He never had a problem.

73,
Darrell, WA5VGO