[Arny Krueger[_4_]]

"Patrick Turner" wrote in message
...

Some sub-minies were used for hearing aid apps, so B+ was not high,
nor was filament voltage and current. But principles are the same.

The circa-1960s Hawk RADAR sets that I worked with in the Army were loaded
with 100's of subminiature tubes. About 400 per unit. Most of them were
used in applications and with voltages and signals that were usually being
performed with miniature tubes. Construction-wise what internals that could
be seen resembled a minature tube with most of the empty room and spacers
taken out. If memory serves a dual diode was the only type with more than
one function. I'm drawing a blank about dual triodes. The subminature tubes
were rated to be highly rugged (they were also used in missles and artillary
shells) and long-lived - at least 10,000 hours. In the equipment I worked on
they were clipped onto heat sinks that underlaid the swaged-post epoxy
terminal boards that the other parts and wireing were attached to. The
chassis were like 19" long sheet cake pans and mounted as back-to-back
pairs in pull-out drawers. Air was forced in between the chassis. The
chassis were held in place by aircraft-style screw clip fasteners and all
connections were via a single multi-pin connector with both shielded and
unshielded pins and teflon-coated silver-plated fine stranded wiring.

The filament supplies were magnetically-regulated 6.3 volts DC while the B+
was highly regulated 250 or 300 volts. The few socketed tubes were power
tubes including 300A series regulators in the power supplies. Air
temperature inside the equipment boxes was up to 140 degrees.