The silicon diode that replaced the selenium rectifier has to be there, but it can hide, it's so little. Probably under the chassis. In the post that I referenced I circled where I put mine, but the last repairman on yours could have put it anywhere underneath the chassis. Here's a picture of one with its schematic symbol. The end with the line is the cathode and that end goes towards the B+ plate voltage of the radio.
http://t2.gstatic.com/images?q=tbn:A...uiSGgwrjC6NHWu