On Wednesday, April 25, 2018 at 6:02:47 AM UTC-4, wrote:

before dull valve emitters were discovered, valves/tubes used thoriated tungsten direct heated bright emitters. They ran white hot. Nuke magnetrons use thoriated tungsten bright emitters.

These must go back to pre-DeForest days??

I have some direct-heat thorated tungsten 00, 01 and 71A tubes, as well as a number of UV99s and similar. Not a one of them gets much past a mild orange.
Not to mention 2A3, 10 and 50s. The closest thing to a "hot" tube I have is a 10, and that filament is about like a 25 watt tube running at 50V or so.

Which tubes are these?

Peter Wieck
Melrose Park, PA