A question I'm sure the experienced amp builders can answer. I was reading
through the Eimac 8874 datasheet last night and found this paragraph:
quote:
HEATER/CATHODE OPERATION - The rated heater voltage for the 8873, 8874, and
8875 is 6.3 volts, as measured at the base of the tube, and variations should
be restriced to plus or minus 0.3 volt for long life and consistent
performance. At frequencies above approximately 300 MHz it may be necessary to
reduce heater voltage to compensate for rf transit-time heating of the cathode
after dynamic operation of the tube has started. The back heating is a
function of frequency, grid current, grid-bias, anode current, duty cycle, and
circuit design and adjustment. The following heater operating voltages are
recommended:
Frequency (MHz) Heater Voltage
300 or lower 6.3
301 to 400 6.0
401 to 500 5.7
:end quote
In my new 70cm amp, my heater voltage is set to 6.3 volts. Reading this, there
are many variables to take into consideration of which there is no "formula" to
figure out the ideal heater voltage. Should I simply reduce my heater voltage
to 5.7 volts? What effect would this have on the amplifier performance? Does
anyone have experience with lowering the heater voltage in this type of
situation?
Thanks,
Paul
kg7hf
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