Diodes including rectifier, high-speed, germanium, microwave...

Brief intro on replacing Selenium Diodes or Bridge Rectifiers with Silicon diodes or bridge rectifiers. Dimension of the plates on Selenium rectifiers is a big clue as to the current capability. A 4-plate Selenium bridge can handle 400mA if the plates are 1" square, 1.5A if the plates are 1.5" square, 4.8A for plates that are 3 inches square, 8.4A for plates that are 4 X 4 inches, and 17A for plates that are 6 X 5 inches.

What are the tabs on Selenium Rectifiers? The middle one is positive, the next ones out are the AC input and the last two which are on each end of the rectifier are the negative terminals and these are normally connected together (shorted) with a jumper wire.

When substituting a silicon rectifier for selenium you may need to consider that silicon is more efficient having only a 0.707VDC drop per diode, whereas selenium are about 5% of the voltage per plate. So a 4 plate selenium rectifier drops the voltage 20% from the AC input. Thus 34VAC becomes 27.2VDC with selenium vs. about 32.6VDC with silicon! You may need to add a resistor to compensate otherwise circuits may run hotter than before...