Dictograph Phono Unit

[phono-farm]

There is a Dictograph Radio Phono-Unit on eBay right now that reminded me that I've got one of these stashed away somewhere, but I'm wondering if these were ever part of a particular machine, or just an accessory to be used on any Diamond Disc phonograph? They might have been most usefull if you didn't have to manually remove the Edison reproducer and install the phono-unit, or vice-versa, everytime you changed what you were listening to.
http://www.ebay.com/itm/221162028168?ss ... 1423.l2649