Variable Transformers (Variac)

I have four variable transformers. One is a General Radio Model W8MT3 Variac shown below. The name "Variac" is a registered trademark of General Radio. Variable transformers are of an autotransformer configuration where one side is common to both the power line and load. As such, it cannot be used as an isolation transformer. Shown next to the Variac, is an isolation transformer. This configuration is what I use to power up old radios and televisions for repair and test.



Another variable transformer I have is a much older General Radio Variac shown below.



Another variable transformer I have is manufactured by STACO shown below.



Another variable transformer I have is manufactured by Philmore in China shown below. This device has a built in voltmeter to indicate the output voltage and is the newest variable transformer I have.