Quote:
Originally Posted by old_coot88
Wonder if there's sufficient voltage across the 1B3 filament to sustain emission. The filament should be glowing a dull orange if you darken the room and can see up inside the tube.
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Great point. And if the 4.7 ohm filament resistor has drifted high it could have exactly that effect. It's usually soldered directly under the 1B3 socket and a pain to get to.