Michael A. Terrell wrote:
snip

Have you ever used a water cooled
power tetrode with two, 1000 A, 1.5 volt filaments? The AC had to match
to a few millivolts, or it would modulate the output current. You had to
use an open ended wrench to adjust the length of a copper buss bar. Its
resistance went up as it was stretched. This was in the RCA TTU-25
series UHF transmitter.

Was that adjustment in one direction only (to increase resistance)? How
much range did it have before the copper would need replacement?

Michael