The most common and most likely answer to this crossword clue is the 15 letter word SERVOMECHANISMS
I've seen this crossword clue in Independent
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Buddy explains!
The straight part
We know that "power amplifiers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case power amplifiers = servomechanisms.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SERVOMECHANISMS mean?
SERVOMECHANISMS noun- A mechanical device for controlling large amounts of power by means of smaller amounts of power and correcting the performance of the device using feedback
- Any system which controls motion automatically using feedback