If the soundbox lettering is at the back then it is later than 1925-26, but I don't know when the new motor was introduced... I'll bet yours is from 1926-27. I believe the motor 59 was introduced in 1928, but I'll have to check the HMV portables book by Dave Cooper.... Also the change of the way of attachment the crank inside for storage.
Maybe any of our experts will jump in to shed some light.
Info for your curiosity: the intermediate hook for holding the crank had originally two legs like the other two, but typically one leg is broken because it was somewhat misplaced at the factory, and suffered from strange tension. A systematic HMV assembly error!
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