The converters which don't work are probably those "el cheapo" switching types which provide a horrible output waveform which in no way even approximates the proper form. They work for lights and other non-critical loads, but are often useless for sensitive electronic equipment. To be blunt, the best place for them is in the trash.
So long as you use a proper transformer-type unit to change from 120 to 240V, you shouldn't have any problems. Of course, with a U.K. 625-line/PAL recorder you won't be able to play back tapes on a U.S. 525/NTSC receiver while there, but that's a different issue.