I use 50VA 2 x 15V toroids from Vigortronix.
http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1675058Easily enough overhead to work at 220V. If that makes you nervous,
particularly if your line voltage frequently falls below 220V, then use
a 2 x 18V.
A 2 x 24V transformer will work but will cause the power supply to
generate a lot of heat which will need to be dissipated by the rear panel.
Also, virtually every Polysix and Mono/poly I have seen has a blown
'spark killer' capacitor on the mains in board. Remove it and don't
bother replacing it.
Tony
http://takla-makan.bandcamp.com/http://www.oakleysound.com