As fasr as I can recall from the far off days when I studied analog circuits,
the major use of diodes in amplifiers and such is to provide a voltage drop
that has the same temperature dependancies as the transisitor junctions.
I've certainly seen amplifier schematics that had otherwise inexplicable
chains of several identical diodes...  As such, there may even be cases
where it makes sense to use an idential transistor as a diode (although
I don't think a cheap N-transistor am radio would qualify.)

BillW