This unit was manufactured in the 1950's and is still in service in many shops.
In the 1960's I used a model like this to repair auto radios.
The unit has switchable average working of voltages of 6 v and 12 v.
The 6 v range has an intermittent current of 20 A and a constant of 12 A.
The 12 v range has an intermittent current of 12 A and a constant of 6 A.
The unit was tested and is in working order.