Need to vent tube heat?

FWIW I have my tubed amps on the bottom shelf of a cabinet. When used the doors in front of the amp is open. In the back of the cabinet I cut openings to accomodate two 120v fans wired in series. In that fashion they move lots of air, each fan at a lower speed. The fans draw the air over the amps and push it out the rear, The noise level is very low and not intrusive at all. After operating all day in about 6 cubic feet of space the amps are 'cool', relatively of course. You can get these fans at an electronics store for about $20 each plus some wire and a switch.

You certainly need to vent tube heat.
Back in the 80s ARC used to make rack ventilation units. The idea is similar to Newbee's, two fans inside a 4" tall rack unit.
The Ref 110 and Ref 210 amps have their own fans, just make sure that the cabinet back has plenty of openings to allow air flow.

Newbee, did you mean 12v dc fans in series? I agree this will reduce the speed and noise of the fan. You can also run a single 12v dc fan on a 6v wall wart and get the same effect.

Zargon, I do use 5" 120v fans - they move a lor of air with less noise and vibration (only) when you use two in series. I've never used 5" 12v fans but I'd imaging the result would be similar. I got into the 120v models because I originally used just one and put it on a rheostat made for a fan (which was just a PITA - it didn't get enuf air movement when it was dialed down enuf to work quietly). The thing I wouldn't recommend is the smaller 12v computer fans. Not much air, lots of noise.

Many years ago I had my components in a tight open face, closed back and sides, shelved cabinet. I cut two holes in the 1/4" rear plywood and installed nearly silent small computer fans, switched to a power bar. At first use, I found a very slight vibration noise was being transferred to the plywood. I added 3/4" reinforcing bracing to the exterior of the plywood which stopped the vibration.

The cabinet was pushed close to the rear wall and collected dust. Within a year I was to changing out the fans because of wear which caused noise.

IMMHO any design with fans should include easy accessibility for cleaning and replacement.

Good Luck