These units are made up of diodes and air or oil cooled variac to control current stepless.
Advantages
i. Rugged and reliable.
ii. Easy servicing and maintenance.
iii. Limited ripple content.
Disadvantages
i. Bulky and space consuming.
ii. Low efficiency.
iii. Slow response to auto process control.
iv. Not suitable for periodic servicing.
v. Susceptible to overheating in air cooled versions.
These units are made up of diodes and air or oil cooled variac to control current stepless.