[Milsurplus] When Were Metal Case Tubes First Produced?

[Todd, KA1KAQ]

On Fri, May 23, 2008 at 8:28 PM, Unserviceable but Repairable
<cosmoline at aa4rm.ba-watch.org> wrote:

> Loaned one to a pal years back.  Pal died & so did the 6D5
>
> Wud like another again

Think I have a couple in the metal tube stash, Marty. If I locate one,
I'll send it your way.

1937 Hammarlund SP-100, second in the Super Pro line, swapped out a
number of the big-pin glass tubes for metal tubes, including the trio
of #42 audio tubes for the 6F6 cans. Remarkable receiver for its time,
still works and sounds great today - metal tubes and all. Later 200
series went all metal.

Was always curious: did the metal envelope cause earlier failure due
to excessive heat, or actually help to sink it away?

~ Todd,  KA1KAQ