If you plan on working on old tube radios, you should have an isolation transformer. This is ESSENTIAL for being safe while working on this equipment.

What is an isolation transformer?
An isolation transformer is a standalone 1:1 transformer for AC mains. It is meant to go between your device and the mains. This is most useful for devices that do not have a mains transformer in them. The isolation transformer isolates the device and you from the mains. It is still possible to be shocked while using one, but it will help with being safe.

How does it work?
An AA5 radio does not have a mains transformer. The vacuum tubes are wired in series and then grounded on the metal chassis. What if you plugged in the cord backwards and then touched the metal chassis while working on it? You would recieve a mains shock.

The transformer causes the radio to ‘float’. It causes there to be no direct path to mains voltage. This means that unless you give it a path to ground, it will be harder to get a main shock – unless you touch both incoming AC lines.

The isolation transformer is not a foolproof way to prevent being shocked. You should still be vigilant in being safe while working on these radios.

Remember, better radio technicians have lost their lives to these devices. Be safe. There is no radio I know of that is worth losing your life over.