This is a high-quality piece of test equipment that is used to form filter caps, bring up new amps on their maiden voyage, and work on amps that are blowing fuses. Yes, we use current limiters around our shop for all the new amps and all service amps. If you are going to do any work on a tube amp, the current limiter is a must. Any time you do service, you start the amp in the current limiter. This will protect the amp from burning up should something be wired wrongly. In the event of a malfunction, instead of the amp blowing up, a light bulb will light up, thus letting you know the amp is drawing too much current. The light bulb limits the current so that nothing will burn up. When troubleshooting an amp blowing fuses, you can replace the fuse and plug the amp into the current limiter. The light will burn brightly. When you locate the malfunction that was causing the fuse to blow, the light will go out.
It has a couple of switches too; one for the AC power and one to change from limit mode to regular power mode. When everything is safe, you switch to full power and it is the same as plugging the amp directly into the wall.
If you are building amps, the current limiter is a must. When powering up for the first time, you should always use a current limiter. Should something be miswired, instead of seeing a mushroom cloud with irreversible damage to the amp, a light bulb on the limiter lights and you know there is a problem without anything blowing up.