The switch removed from the old tuning units (TU-???) is similar to a switch
made by Radio Switch and was designated as a radio Switch Model 65 Switch.
It is rated at 4500V peak flashover at 60 cps (yes cps, old catalog) and 25
Ampere current carrying capacity.
Another method is a small rotary switch that selects a much larger relay
(or contactor) wired to each primary tap. Needs a minimum of panel space
but requires larger space somewhere in the power supply area close to the
primary (hopefully). The Model 65 can be found at most swap meets here in
the US.
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