Offered here is a Selenium Rectifier replacement for the Zenith Transoceanic and other applications that use low power selenium rectifiers.  This replacement features a 600 V silicon diode in series with a voltage dropping resistor.  The resistor is included to prevent overvoltage in your radio due to the improved rectification efficiency of the silicon diode.   The replacement includes a 1 inch standoff to mount the replacement in place of the original selenium rectifier.  Simply reuse the original machine screw, washer, and nut.  See photos.  The second photo shows a selenium rectifier to be replaced in a Zenith H500  The third and forth photos show the new rectifier installed in its place.  Note the polarity of the old selenium rectifier before disconnecting it from the radio.  The wire connected to the "+" mark on the old selenium rectifier (in this case a power resistor) must connect to the terminal marked "+" on the replacement.