What do you mean by simple receivers ? What are you trying to receive,
with what stability and sensitivity ? Amateurs have traditionally used
crystal-controlled downconverters in front of lower frequency
receivers, but this is generally suited only for receiving small
segments of spectrum and doesn't usually have a very small parts count.
The local oscillator usually involves several multiplier stages and
tunable filters. The performance can be very good though.

For example there are lots of technical articles at

http://dpmc.unige.ch/dubus/index.html

The 1N5711 schottky diode works well in the lower microwave range and
is quite widely available and cheap.

Steve VE3SMA