Jinx, power ultrasonic discs are always attached in a press type of mount,
usually two sandwiching a donut copper electrode the other wire being the
chassis and the bolt that goes through the assembly (w/o touching the
middle donut).

I don't know what ultrasonics you tried to desolder but in general when
soldering directly on devices turn the iron thermostat way down and
increase slowly until solder just tacks. Some ceramics are destroyed by
local heating and could shatter or crack. They need preheating in a oven
before soldering.

Peter

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