[R-390] Physical Height clearance: 26Z5W vs 12BW4 vs 25CT3

[Tom Bridgers]

Beyond the rewiring of the R-390A power supply sockets, one other important
issue to consider is that the 12BW4 and 25CT3 are each taller than a 26Z5.
A 26Z5 tube extends a tad more than 1 3/4" once it is seated in the socket.
In a similar comparison, a 12BW4 is 2.3" tall and a 25CT3 is 2.87" tall.

I bring this to your attention because after converting one of my power
supplies to 12BW4's, I was disappointed to find that the tube extended to
just a tad above the horizontal plane normally occupied by the R-390A's
bottom cover.  Had I reinstalled the bottom cover, the top of the tube would
have been snug up against it.  It was easy to see that there could be many
unanticipated situations where the bottom cover might be accidentally bent
slightly inward and thereby breaking the top of the tube.    Clearly the
25CT3 at 2.87" of tube extending above the socket completely eliminates the
option of reinstalling the bottom cover.

If don't want to reinstall the bottom cover, then the 12BW4 or 25CT3 will
work just fine.
73's,
-tom  KE4RHH