Crossword Genius

Musical guides? They used to be on buses (10)

Ross

I believe the answer is:

conductors

I'm a little stuck... Click here to teach me more about this clue!

'musical guides?' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe there's an association between them I don't understand?

'they used to be on buses' is the wordplay.
I cannot quite see how this works, but
'to' is found in the answer.
'on' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Guardian.
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