Hi Gooner and Roof,
24a you are looking for "Hobnob" as a noun (as you might see in a supermarket) - It's a 3 letter trade name of a well known pen/writer + the 1 letter notation for "the big man on board" (think a game) around the usual 2 letters for "that is".
4d Does not end in a P. The definition is "element" (think 'periodic table') - I think it's meant to be "the essential" letters in "musical" but, in order to get the symbol for the answer you have 2 letters before it and 3 after, which looks a bit odd.
14a is not a bird, Ruth. The definition is "warning light" and is a 2 letter abbr. of a 'flier' (think 'airline') around a 1 letter abbr. for "electronic" + a 3 letter word for "against".