Wow - it belonged to your great great grandfather! But.. it isn't a concertina. It's a three-row diatonic button accordion. Button accordions aren't the focus of this web site, but we're a friendly bunch, some of us play button accordions, and we'll offer what help we can. Do you have a picture of it you could post for us?
On the right hand side, each row is like a separate harmonica in a different key. You'll probably find that the keys are a fourth apart from outside to inside, for example G-C-F (G would be the outside row) or A-D-G. There are many key combinations, even Bb Eb Ab.
Hohner is still making new button accordions, and they are still a popular brand. They have a reputation as solid instruments that you can get a lot of music out of. I don't know a lot about Hohner button accordion history, but sound quality and responsiveness seem to vary dependiing on the particular model and when it was built. My oldest button accordion is a Hohner Corona II in G-C-F from about 1950, and to my ears it has a really sweet sound.
By chance do you know what kind of music your great great grandfather played? May we hope that you are thinking of keeping this button accordion and learning to play it?
For a quick gathering information, just type "button accordion" or "melodeon" into a search engine. For a start, you may want to look at the Button Box web site (http://www.buttonbox.com) - they also have a list of links to other sites. Another similar site that comes immediately to mind is Hobgoblin . They have stores in England and in the U.S. -
http://www.hobgoblin.comAn instrument that old may well need some attention. Concertina.net members who also play button accordion (and there are a number of us) will be happy to suggest repair people if you are interested.
You may also want to check out a "new" web site for button accordion aficionados that Lester Bailey just told us about: http:www.melodeon.net.
Regards,
Brian