Hi Ethereal,
19d - Is an alphabet clue.
20a - 4 letter "ale" + 3 letter "container" + A (from the clue) - definition is "a large piece of brass" (instrument)
23a - 2 letter "good old" + 5 letter "pancakes" minus last letter/'finally disappeared' all inside 4 letter "cookers" - definition is "frightful apparitions"