I owned my poor old 1967 Silvertone by Harmony for over 45 years and currently it's in the hands of Robert Stoner who is breathing new life into it after all the years of abuse it suffered in my "care."
What guitar have you owned the longest and do you still have it??
Well, yes, I mean, the finger posisitions are radically different. But, if you play mandolin or Uke, you probably cope with different chord forms, and the same goes for common guitars if you use open or dropped tunings. But triads always have a root, a dominant and a middle note, no matter what instrument you play...
If you have a look on my vids, "Yesterday" is played in the key of D, "Greensleeves" is played in E minor and "Fado Alberto" is in B minor. The hand positions for the chords are totally different, but your ears will recognize the chords, because they sound pretty much the same as in common guitars, only higher - as if you were using the "Nashville" tuning.
This said, bear in mind that Portuguese guitar is NOT a strummed instrument like Dixieland banjo or rythm guitar. That means you almost never play 6-string (12-string) chords. That's why you won't see me use barré chords, they simply are not necessary. If you play a 4-string (8-string) chord, you'll get plenty of sound, there's no need for more... Furthermore, P-guitars have tremendous volume, I may be playing a single-note solo with my bare nails, and have a Martin Jumbo strumming flatpick chords backing me, and still my P-guitar will be heard loud and clear, above the accompaniment... pure magic!
Second warning: P-guitars are highly addictive!
My 1968 Martin D-35 which I am holding in my picture. My girlfriend (and wife now for 43 years) had a very good friend who was dating, and later married, one of the D'Addario brothers of guitar string fame. One day Richie says hey, do you want me to get you a guitar and I said sure. As I remember he showed up with the Martin and asked for $350, how lucky could I have been. So 44 years later it is still my favorite guitar, apologies to my 4-year old Seagull Performer QII. I even have it in my will for one of my sons. I joke with other players that as it ages the guitar just keeps getting better every year and its player is trying to keep up.
My first actual guitar was a 1964 Harmony BobKat w/ 2 pickups. I still have it, but it is in serious need of repair. The pickups broke, and it became a project that never got completed. I have a pic somewhere with me using it at a gig way back then. Funny, I learned 4 chords pretty well, and barre chords, major and minor variations, and was off and running. My band or combo, as it small bands were called back then, became pretty popular. We played a mix of pop, rock, and a lot of soul music. We were lucky and scored a steady gig at a KC downtown USO that held dances every Saturday night for servicemen and women who were mostly on R&R from serving in Vietnam. Soul music was very big with those folks, and we loved playing it. We had an electric sax player, organ player, and even a female vocalist. We covered everthing from Beatles, Hollies, Kinks, Stones to Martha and the Vandellas, James Brown, Booker T, and Sam and Dave, and more...
That little BobKat served me well, until I saved up enough money to buy a Rick 360 and Vox Super Beatle.
This Höfner jazz-guitar was a gift from my father in 1963 ( next year this baby will be 50 years old!!! ) and it was never repared,although I made some changes on it ( I renamed it as DOC ).
On the picture,my partner and friend ( Mr. Jorge Custódio ) is picking some swing tunes ( we got a duo = LISBON SWING MANOUCHE DUO ).So,this is the guitar I owned for the longest period of time and it plays nicely ( never out of tune = german product ).