Take a good look at the detailed roses and other floral patterns pressed into the cabinet. Although there isn't a photo to show it in this post (there is a forthcoming post on reed plate markings), the aluminum reed plates in this accordion bear the Koch trademark (a friendly mountain goat in profile). It is in GC tuning with accidentals and the bellows are attached to the instrument with large screws that travel through the cabinet from the faces on either side. There is buckram or fake leather (it is so old and dry that I cannot tell which it is so I'll call it buckram) on the ends of the bellows. This accordion was built before the modern bellows design came about, whereby the bellows are attached with small pins. You can see how that is in the making here - simply extend the width of the cabinet to the edge of the bellows and you have dimensions that are very similar to today's accordions.
Below is a shot of the grille and keyboard. You can see the screws that secure the bellows on either side of the grille. These travel through the cabinet and terminate in the bellows frames. They are plain old wood screws with big sharp threads, not machine screws fitted in threaded sockets. The buttons are the old style, round circles that are fixed at the center to wooden levers. Behind the grille, the wooden levers are connected to a cheap action made by metal rods that are easily bent, and those are soldered to metal pallets, which are bent just as easily - hardly an ideal design for a treble or bass action.
Below is a very similar accordion, also built by Koch. This one is interesting to me because it has a metal grille in the same pattern as the one that is used on today's 2915. The keyboard cover has oak leaves along the inner edge, a feature shared with the presswood pokerworks built by Hohner. The bellows are flanked with the buckram stuff like the model above and there are decorative metal corners. It has more contemporary styled buttons, not the old style ring button faces. This accordion was sold on Ebay (Deutschland) last year.
Below is another presswood pokerwork made by Koch and bearing the company name. The attractive mountain goat trademark is proudly emblazoned on the front of the cabinet. Too bad Hohner kept the Kalbe anchor instead of the Koch mountain goat! This accordion has reeds for a single key, tuned similar to the Hohner 1040. It has bellows like the two-row in the photo above, note the buckram and metal corners. If you look closely, the pattern burned into the edges of the keyboard cover is the same one that is used on the Concertone in the first two photos of this post. It has a square keyboard but old style buttons and wooden levers. The bellows are attached in a now-archaic screw-and-pin mechanism. I think this mechanism is a better idea than it appears to be. The company has to pay more for the metal pieces (contrast these big clunky things with the cost of four tiny bellows pins), but the screws pull the bellows to the cabinet and keep pressure against both mating surfaces. This accordion belonged to the late Ray Laforest and the photo is from his website.
Here's a cool box: a Koch presswood pokerwork two-row, four-stopper. It's the best of both worlds. Note the familiar design decorating the keyboard, shared with the Concertone and the model above. The keyboard is also the same as the Concertone, so are the wooden levers and the buttons. But on this model, because the pallets are shown off outside the box (not hidden behind a grille where corners can be cut), the metal levers attached to the wooden levers are of a higher quality and not the cheap metal things fitted in the Concertone. The pallets are better, too. If I remember correctly, I downloaded this photo from a forum post by member triskel at melodeon.net. Shoot me an email if you'd like me to delete it.