Which diy valve amp without valve sound?

[grovergardner]

BTW how can the tubes be protected against picking up vibrations from the speakers? In many amps the tubes sit on top of the case without any covering...

There are tube coolers and rings made to reduce the microphonics. Some builders mount the tubes on cushioned sockets that isolate the tubes from the chassis. I usually avoid metal altogether and use a Delrin top plate. Not only is it easy to machine, but it eliminates any sympathetic vibrations from metal top plates. The difference is quite audible.