RadioGuy wrote:

Well, the tube (6146) was in constant production during Drakes operation
(about 30 years) so it would imply that they were very common and
cheap---practically every other amateur equipment manufacturer was using the
6146.

Not quite. Yaesu used sweep tubes widely as did Swan, WRL, National,
Heathkit (in some transceivers) and even Hallicrafters (in some
transceivers).

Large numbers were used by the military and commercial services. My
gosh... if Heath was using them they certaintly couldn't have been that
prohibitive to design with. So it begs the question why Drake was using
them.

They likely got really good prices on them. In addition, a pair of
6146's was good for 80-100w output. A pair of 6JB6's in the Drake T4-XC
was good for about 140w. Swan and WRL pushed a pair of other tubes to
even higher output.

Dave K8MN