Although there are several resources on the web (1, 2, 3, 4) on how to convert a RR501 transceiver from 110v to 220v I recently (mid 2010) bought a new one that had an updated circuit.

Using Ido Bartana's guide as a base and these general tutorials on 220v module modification (1, 2) I ended with this set of steps

• Change the large blue, (2E225) from 1uF/250V to 470nf/400V
• Change the smaller blue, (2E224) located close to the output connector, from 0.22uF/250V to 0.1uF/400V
• Change the 130V MOV in parallel with the input to 250V RMS. If you have 230 or 240V use 275V RMS
• Change the 330k 1/4W resistor going to the output connector, to 470k 1/2W
• Add a 100 Ohm/1W resistor in series with the 110v cam relay coil