This interesting item arrived to have a new mains cable fitted. It’s a self adjusting variac or sometimes known as an auto transformer.
Instead of the usual control on the top to set the required output voltage this one has a small motor and gears to move the variac wiper position to obtain a preset output voltage.
In effect it’s a fixed mains voltage regulator which in this case is configured to provide a 100 volt output. An unusual voltage but vintage HiFi built for the Japanese market requires 100v so this does the job.
Using a variac provides the nice clean output you need for quality audio equipment without any of the possible noise you might get from a switch mode power supply.
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