Four of the unclued lights (one of two words) and an unclued pair are of a kind, and can become the remaining unclued lights, including a pair.
 

Across

 
1    This song of praise would become heathen with a change of note (5)
6    Failure of old skinflint at university (7, hyphened)
11    Catlike print he has developed (10)
17    Tramp’s symbol (7)
18    Tolkien creature at hospital? (3)
19    Perform rapid chords, rearranging gig with a repeat (10)
21    Tentative effort producing sort of chain letter — always (5)
24    Star sign regularly appearing for triplet (4)
30    From which to serve...