Dear Tom,
The question of 5.00 or 5.50 volts on the filaments of
3CPX1,500A7 triodes was very interesting to me when
designing an HF amplifier two years ago incorporating
these devices.
Letters between Eimac's Mr. Brandon and myself ensued
because the published tube data sheets were clearly indicating
5.50 volts.
The 'CPX's can be used in basically two ways: Pulsed and
Continuous service. The pulse service sees an incredible
amount of anode current and a huge power output capability,
albeit with pulse widths and durations measured in
microseconds.
As explained to me the 5.50 volts filament supply is used
specifically in Pulse Service, and the rating of 5.00 volts
is used in continuous service. What was emphasized that
if the tube is in continuous service like Class AB linear
service, was that the filament voltage be closely monitored
to not exceed plus or minus ten percent of the rated voltage.
Additionally emphasized was that the tubes benefit by a method
of current limitation on cold startup.
Tom, I followed up with all this because a new set of 3CPX1,500A7
triodes broke the bank at $1.4K each, and if there is any way of
milking life out of them it was worth incorporating such
measures into the design.
Lastly, Eimac publishes a technical bulletin for maximizing tube life
through the measurement and control of filament voltage whereby
emission is used as an indicator, with the tube heater set at just the
point where the "knee" in emission increases, and then just under,
maximizing the tube life, and further, Eimac has a plan whereby this
adjustment can be brought to bear in the last hours of service, both
indicating
a need to start the purchase process for replacement and also adding
many hours of useful life.
Respectfully,
Hal Mandel
W4HBM
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|