Apologies, Clive, for not answering you sooner. I don't seem to be getting notification of replies to my post. Dan, (see above), has found the manual for it, but here is a picture of the inside, for the record: You can see where the cartridges would go. Steve. Thanks Dan, Well found! I'd done a lot of googling without finding anything. My one is subtly different, in that it doesn't appear to have any controls. I'm going to get in touch with pr-electronic and I'll post here if I find out anything useful. Steve