Philco Mystery Control Receiver

[dtvmcdonald]

Have you considered that modern power line interferene is simply so
strong it fires the thyratron?

To see what it takes to keep it off, simply put a battery in series with the 50k
resistor in the grid lead. Try 2 to 15 volts, negative to grid.

Use a scope to look for noise pickup in the amplifier. Use an
isolation transformer of course.