How should one replace these just with one diode? I have an old viking and someone has put a diode across the selenium rectifier. I assume that is because it is gone??

:How should one replace these just with one diode? I have an old viking and someone has put a diode across the selenium rectifier. I assume that is because it is gone??

Selenium diode forward voltage drop can become excessive with age. I think 30V is typical for a good selenium diode. I usually use a 47 ohm, 5 watt resistor in series with a silicon diode. Otherwise the high efficiency of a silicon diode will result in excessive B+ voltage. Putting a silicon diode across the old selenium diode is sometimes found in old repairs. It works Ok, but not recommended.

Richard

::How should one replace these just with one diode? I have an old viking and someone has put a diode across the selenium rectifier. I assume that is because it is gone??
:
:Selenium diode forward voltage drop can become excessive with age. I think 30V is typical for a good selenium diode. I usually use a 47 ohm, 5 watt resistor in series with a silicon diode. Otherwise the high efficiency of a silicon diode will result in excessive B+ voltage. Putting a silicon diode across the old selenium diode is sometimes found in old repairs. It works Ok, but not recommended.
:
:Richard

I agree completely with Richard's advice. I would only add one thing: do not "bridge" the old selenium with the new series diode/resistor combination, but make sure you disconnect the old selenium from the circuit. In other words, leave the old selenium rectifier in the chassis but disconnect one of its terminals to isolate it from the circuit. The remaining terminal can be used as a tie point for the new components. The 47-ohm series resistor Richard suggests is a good starting point. It can be adjusted later if necessary to get your B+ and/or filament voltage at the the proper level.

Poston