PeterD wrote:

On Thu, 12 Nov 2009 00:05:44 -0500, "Michael A. Terrell"
wrote:


msg wrote:

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?


The originals were still in the transmitter, and it was built in
1952. Backing the bolts off allowed some change in length, so they were
backed off and then set to a minimum torque. The new tube was
installed, and the voltage measured. Then each was tightened to the
recommended filament voltage. A new tube would last a couple years, so
it didn't have to be done very often. What bugged me was 3 KW of
electricity was used to get 25 KW out of the tube.

Amazing, isn't it! g What was used to measure the filament voltage
with that accuracy?


An RCA VTVM on the lowest AC scale. If the needle moved at all, it
was out of spec. Yo connected it to the filament end of the pair of
copper resistors and adjusted for zero volts, like a Whetstone bridge.
That transmitter was built in 1952.


--
The movie 'Deliverance' isn't a documentary!