Possible Clues:

• Informer linked with seedy bar's sudden decline
• Steep vertical plunge
• Calamitous decline
• A sudden drop, so I need changes involving volts
• Video sent endlessly for broadcast showing steep plunge
• Proceeded gingerly at quarter past four having made headlong plunge
• Disastrous drop
• So restricted, obvious one will shortly turn and plummet
• Numbers need editor: the crossword setter's taken the plunge
• Steep drop, as in prices