Daniel, did you buy the set as "New" (even if "new-old-stock") or second-hand? If your Stainz loco has the slide switch in the cab, then it won't be one of the very old versions that PhilP mentions above, but it could still be a set that has been in shelf stock somewhere for a good while. To help identify the exact version of your loco, what is the model number (most likely white numbers on a black sticker) underneath the loco.... and also does it have a small (about 3/8 inch) round GOLD sticker, with a 6-number code on it? If so, what is that 6-digit code?
Jon.