In a message dated 3/1/2005 10:49:36 A.M. Central Standard Time, r@somis.org
writes:
In the AL-1500 diagram, the cathode is connected to one side of the
heater, C7 couples RF from the tuned-input to the cathode ,and C8
couples RF from the tuned-input to the other side of the heater. Can
someone please explain why the heater is driven with RF?
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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The most likely reason is to limit the voltage between the heater and
cathode. If the filament was not tied to the cathode there could be rf voltage
on
the order of 90v peak or more between the cathode and filament. I didn't see a
specification for this in the old data sheet I have here. A breakdown test
could give a hint here.
Also, if the cathode became open circuited for some bizarre reason, like the
series cutoff bias resistor opened up, the cathode voltage could rise to
near the plate voltage. This would not be good for the cathode to filament or
cathode to grid interface.
Was this a trick question?
73, K5GW
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