Tube amp on the floor or on the rack?

You should have a shelf/sand box of some kind under it.

Get audio points and set the amp on those, and then put it on the floor. Try that then try just putting it on the ground, I don't notice a difference personally. FWIW I am friends with the owner/designer of a highly regarded tube amp company and he laughs at people who use spikes and such. His amps start at 30k and go up from there so I am sure he know a thing or two about what he is talking about. Just make sure you don't have it in a rack that doesn't allow the top of the amp to cool and heat what ever is above it, that would be a concern for me before the bottom cooling.

Tim
btw I have my VK-60 sitting on the floor between my speakers-nothing else between them. For the simple reason it looks cool and is very functional.

Tube amps=floor and try to keep it as immune as possible from vibrations, see that the airflow around it is not impeeded and beware of thick carpets. That's at least what I learnt through the years. Cheers,

Thanks for all the input. I don't have the luxury of a
dedicated listening room, so it doubles as the family
room. For that reason, my amp on the floor isn't really
safe. My rack will actually accomodate the VK-60, and
I would put it on the top shelf. It's an open design,
so air flow won't be a problem. It's either take my
chances on the floor or stow it safely on the rack, so
I'm trying to decide which way to go.

You might want get some type of cage for that thing, if it doesn't have one. Kiddies and pets don't do well breaking tubes and burning themselves. (I don't know your situation). The only problem with "up high" is-it can fall that much farther, not to mention when the heaviest piece is on top it will create more instability should the rack get knocked. Keep it off the floor so it will need be ventilated. And a good amp stand will do that and provide some vibration immunity, of course as heavy as it is its own weight will help that. And some type of cage protection would help.