[morzh]

As I remember selenium bridge rectifiers, the "+" sign was in fact at the positive output. They used the wrong symbol for it, but the "+" sign is at the right place, which in case of the selenium element would be at the Cathode (negative). However a single diode, of course, installs with its triangle to the AC input and with its bar to the output. We just have to make sure we do understand the marking. If it is a regular today's diode there will be no "+" sign, but the Negative (the bar) will be marked with a bar and this is what connects to the load, and the unmarked end connects to the AC.