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?
If you have a 12v trigger on your pre, you can run a small PC type cooling fan directly off the trigger output. Check the current requirement of the fan against the current available on the trigger. fans.html Then in search box type silencer. About half way down you'll see 8x8 ball bearing case fan 11.95. just above quiet fan shootout,read it ..i got 2 of these had a wall wart laying around ,went to radio shack,and got little black box for switch,put velcro on back of box and shelf to hang it i can cut it off,,made a wooden fork like hanger to slide on back of self and mounted fans ..these fans a so great you cant here them run the shoot out ..greaest treak i know of for cooling..i set mine on my ps audio p 300 and it shays so cool befor it got hot even with there fan in it,shit works
just wondering which modl computer fan you picked up, tried to find it on the web site but wasnt sure,thanks try that im sorry they changed there web sight around..they went down in price get a couble of them .i had a 12 volt ..800 milla amp wall wort around and have 2 fans running off of it dant need 800mas 400 would do.i even got some 2 prong male and female plugs from radio shack and hook 16 gauge wire from each fan about 2 feet long so i could move them around and then unplug them also..hard wired both fan wires in black box where a switch was mounted box is 4 inches by 2 inches maybe..rect in shape,and ran the power wort on other end of box...i did by a 1/8 male and female plug ..over kill but clean
Sounds like a good possibility. Note the fans you mentioned are about 3" X 3" X 1". Hopefully I could mount them in the space I have - but I would be close. I might try to find something even a bit smaller. Just to answer a couple of the questions above, I have vintage tube gear-Marantz model 9 amps and a model 7 preamp. There are four EL34s for each amp and they run in a row parallel to the back edge of the shelf on which they sit. Just measured and I have only 3" from the top of the tube cages to the bottom of the shelf above. Presume the wall wart referred to is the 12v 'cube' that plugs into the wall??