Possible Clues:

• Plucky types may use one, subject to current availability
• Urge late critic developed to get instrument
• Let critic argue for arrangement that needs amplifying
• Possibly alter circuit, e.g. for this instrument
• Instrument Bob Dylan was once booed for playing
• Ingredient for making rock -- mix it with treacle and put in three parts of rice and two of gum
• One depends on current supply as source of rock
• Musical instrument
• It takes pluck to play this, currently
• A feature of rock CD that needs plugging