[R-390] 26Z5W replacement

[Tim Shoppa]

> Thanks for the link!

You're welcome!  One side-thought:

Most of the tubes in R-390(A)'s show up semi-regularly
in large lots of JAN tubes on the surplus market.  I believe
(mostly backed up by hamfest rumor and speculation) that the military
surplused most of their receiving tubes in
the 90's and that a couple of dealers bought extremely
large lots of JAN NOS tubes that they sell off in small chunks.

Of course, it's the ones that don't show up in the dealer's
cheap stocks that we think about substiuting.  Still, there seem
to be plenty of sellers with JAN 26Z5W's and ballast tubes
out there, it's just that the prices are uncomfortable!

The 12BW4 (and 2*12BA6 in place of ballast tube+2*6BA6
and other semi-common substitutes)
do not exist in the military surplus stream and while they aren't
exactly rare, you don't see dealers with thousands of new ones
all in one place.  They seem to be a bit more onesy-twosy from
old radio shop stocks.

Tim.