Clue: Wartime show mounted to conceal a fiddle (5)
Answer: AMATI
Explanation: Definition: fiddle
An envelope ('to conceal') of 'a' in ITMA (even I can say that it is a bit before my time; ITMA – It's That Man Again – was a popular radio comedy programme featuring Tommy Handley which was broadcast during and a little after the Second World War), all reversed ('mounted' in a down light), for the family of violin makers (or, as the clue indicates, one of their products), most famously Nicolo. I suspect that some people have learned a lot from a five-lettered answer!