I might have missed this mentioned.
Using the Hall effect sensors, just run BOTH filament leads through it so the AC filament current cancels, leaving the DC component for the sensor to pick up. Any residual AC that shows up on the Hall sensor is your HUM component. So just arrange LP and HP filters for two OP Amps to separate them out for readout.
Using the Hall effect sensors, just run BOTH filament leads through it so the AC filament current cancels, leaving the DC component for the sensor to pick up. Any residual AC that shows up on the Hall sensor is your HUM component. So just arrange LP and HP filters for two OP Amps to separate them out for readout.
I wouldn't mount any of the classic "sealed" meters, like old Navy surplus Hickoks or similar, directly to chassis in this use. I might try some of the Bakelite cased Weston 301 series or similarly constructed Westinghouse's, but only after testing real hard (safety issues).
But any could be used if sealed up in plexi so no fingers could contact anything scary, and everything floated up above chassis - Old Skool ham construction.
All good fortune,
Chris
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