[HBR] Regenerative communications receiver

[Martin Marris]

>>How do you find working with subminiatures? They look awfully small and
fragile.<<

It might seem that way, but it's the opposite. They were used at the
tail-end of the tube era in high-reliability situations such as missile
guidance systems (inside missile nose cones) or high-altitude aircraft gear.
You can subject them to the sort of vibration and other stresses that larger
tubes cannot handle. See, for instance,
http://frank.pocnet.net/other/Sylvania/GuidedMissileTubes.pdf (this may be
slow to load).

When using them in homebrew gear, you can wire them into the circuit much
like transistors because they have long, flexible leads. The 1AD4s I am
using are cheap (about $2 each from some suppliers) and abundantly
available.

I took a break during writing this email to put a 1AD4 on the hard-tile
kitchen floor, and then stepped on it, putting my entire weight on the tube.
Nothing happened. I've never tried to do that with a conventional, larger
tube -- maybe it would survive too, but I'm not so sure.

A sub-set of these tubes was designated as "reliable" by the U.S. military,
meaning, actually, almost indestructible. The Raytheon catalogue for
"reliable" tubes has pages and pages of the "torture tests" that these tubes
went through before being certified as "reliable."

Strange but true; and quickly eclipsed by solid-state.

Martin