Small circulating fan to cool amps

I have two tube amps that are on a rack system with wood shelves. Because of the space requirements of all the components on the rack, there is not as much space as I'd like to see between the top of the amps and the under side of the shelve above. Although I have not had any problem to date, I'd like to make sure it stays that way. These amps do throw a fair amount of heat. Has anyone had any experience with a small fan that could be used for ventilation? I looked at Radio Shack and although they had a number of small fans, the smallest and lightest ones were 12v. I'd much prefer to run off wall current, but I don't have alot of space in which to situate the fan. Their non-battery fans were just too big and heavy. Any suggestions?