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Tube sets that use a VDR the thermistor resistance DROPS as it heats up, more modern sets that use only a thermistor are the opposite.
In modern. seTs the thermistor is in series with the degausing coil, in old seTs the degausing coil is in parallel with the thermistor through the VDR.
When the thermistor is cold resistance is high and voltage drop is high! As it quickly heats up the voltage drops below the threshold of the VDR. The VDR basically acts like a relay cutting off almost all current flow through the degausing coil to eliminate magnet interference
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