Just saw the mellotron documentary "Mellodrama" the other day. It's pretty interesting throughout with Jon Brion & Michael Penn speaking eloquently about the chamberlin (the US, and original, version of the UK mellotron). It was both a great history and business/marketing lesson, with a lot of technical info as well. Mike Pinder & Rod Argent were interviewed, but (IMO) too much time was spent talking with metal practitioners.