Without valves like this to cover small gallery (5-5)
I believe the answer is:
solid-state
'without valves' is the definition.
I can't judge whether this defines the answer.
'like this to cover small gallery' is the wordplay.
'like this' becomes 'so' ('like so').
'to cover' becomes 'lid' (lid is a kind of cover).
'small' becomes 's' (abbreviation - e.g. clothes size).
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'so'+'lid'+'s'+'tate'='SOLID-STATE'
Can you help me to learn more?
(Other definitions for solid-state that I've seen before include "Using semiconductors" , "using only chips?" .)