Tom says:
>Get that voltage from the same transformer that supplies
>anode voltage, and use a shunt regulator.
If the dissipation is going to be high in the dropper, a constant current source
feeding the shunt screen regulator from a lower voltage can have the same
effect. The current can be set to the maximum allowable screen current, and the
shunt regulator absorbs any excess. Just a variant on Tom's method.
>Use the bias and blower voltage (with an air pressure switch) to turn on the
>HV system.
Question: is pressure the best thing to monitor, or is air flow as good? I was
thinking in terms of a small fan driven by the air stream. Attached to the fan
is a disk with a set of holes in, and the disc rotates between the jaws of an
opto coupler. Unless the frequency of the chopped output from the opto coupler
exceeds a certain critical value (corresponding to a particular air flow) the HV
and filament are inihibited. It requires a 74123 monostable, one R and one
C.......
As the air pressure drop is relatively small for many tubes, this seems to me a
way to measure actual airflow. Is this is as safe as trying to detect a small
pressure drop? It seems, on the face of it better, in that a blocked plate
cooler will give plenty of pressure.
Comments?
73
Peter G3RZP
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