|[AMRadio] HRO question for the day|
ROLYNN PRECHTL K7DFW
k7dfw at clatskanie.com
Thu Dec 17 18:09:27 EST 2009
Interesting idea, as in boiling off fewer electrons to pile up around the
cathode? not clear to me what effect that would have one way or another.
I'm using one of the diodes of the 8B10 as a detector. I found that audio
fidelity of detected weak radio stations can be improved by using reduced
heater voltage. This lowers "contact potential" on the diode, which comes
from stray electrons floating around the hot cathode. Less of this means
that a weak signal doesn't have to overcome as much of this potential to be
detected linearily. I used a 100 ohm 1 watt resistor across the heater to
drop the heater voltage from 8.5V to about 7.7V. This resistor divertes some
of the series string current from the tube heater, thus lowering the voltage
and thus the heat on the diode cathodes (and also the triode cathodes too,
but the circuits they are in didn't suffer). This is just like the reduced
heater voltage on detector diodes like the 6H6, 6AL5 or 5896 to improve
detector performance on weak signals. Less "contact potential" for the
signal to overcome. This should increase the fidelity of AM detection. The
5896 below is a dual diode version"
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