ok c'est en anglais mais je ne saurai triop conseiller la lecture de cette page sur cet excellent site
http://www.provide.net/~cfh/national.html#new
Duolian Metalbody vintage Resonator, 1930-1938.
Collectibility Rating: Squareneck: D-, Roundneck: C (a great sounding single cone National, but they made TONS of them since they were only $32.50 brand new).
Single cone resonator, Steel body, round shoulder, upper F-holes, unbound fingerboard, dot fingerboard inlays
.
1930 Duolian Introduction specs:
Steel body with flat cut f-holes.
Ebonized maple fingerboard with no binding.
Round mahogany neck.
12 frets clear of the body.
Slotted peghead.
Flat fingerboard radius.
"National Duolian" decal on peghead.
"Frosted Duco" finish with crystal-like texture, color varies from grey to green to black.
1931 Duolian specs:
"Duolian" stamped in face of peghead replacing decal.
1933 Duolian specs:
Rolled edge F-holes.
Square neck available special order.
Late 1934 Duolian specs:
14 frets clear of the smaller body.
Basswood neck replaces mahogany.
10 inch fingerboard radius.
"Duolian" decal replacing stamped "Duolian" name in peghead.
1936 Duolian specs:
Solid peghead.
1937 Duolian specs:
Rosewood or "Red bean" fingerboard.
"Piano" body finish, simulating walnut grain.
1938 Duolian specs:
Pickguard added. Sometimes black, sometimes wood grain with diagonal stripes.
Duolian catalong discontinued 1938, replaced by the Collegian. But later 1939-1941 National Duolians were made
National Triolian Resonator Guitars
Description: National Triolian Resonator Guitars
Available: 1928 to 1938.
Collectibility Rating: Polychrome Metal body Roundneck: C+, Sunburst Metal body Roundneck: C, Metal body Squareneck: D-
(At $45 new, it was fancier than the $32.50 Duolian, but still very common. And the maple neck doesn't sound as good as the mahogany neck Duolian.
General Comments: Single cone resonator with a steel body and maple neck. A basic National single cone resonator guitar model. A good sounding guitar, just not very fancy. I especially like the 1929 to 1935 metal body Triolians with the Polychrome finish and the black stenciled Hawaiian scene on the back. I would really like to find a 1934 National Triolian in Polychrome with 14 frets clear of the body!
Late 1928 Wood Body National Triolian guitar Introduction specs:
Wood body, Maple fingerboard, no binding, Round maple neck, 12 frets clear of the body, Slotted peghead, Flat fingerboard radius, "National Triolian" decal on peghead, Multi-hued Polychrome tan-yellow finish with pink & purple highlights, Opaque neck & fingerboard finish same as body, Decal on back was first a flower bouquet, then changed to a hula girl. Last few wood models have stenciled Hawaiian scene.
1929 Metal Body National Triolian guitar specs:
Steel metal body, Maple fingerboard with binding, Walnut sunburst finish or Polychrome tan-yellow finish with red & blue highlights, Sunburst models have ebonized fingerboard, Polychrome fingerboard finish is clear with faint red & blue highlights, Stenciled black Hawaiian scene with orange sun on back, Bakelite neck used 1929-1930 but discontinued due to warping & cracking (no binding), Flat cut f-holes.
1930 National Triolian guitar specs:
Polychrome body finish changes to pea green with faint highlights, Polychrome fingerboard finish changes to ebonized black.
1933 National Triolian guitar specs:
Rolled edge F-holes, Square neck available special order.
Late 1934 National Triolian guitar specs:
14 frets clear of the smaller body, Round basswood neck replaces maple, 10 inch fingerboard radius.
1936 National Triolian guitar specs:
Solid peghead, Polychrome and sunburst body finishes discontinued, "Piano" body finish, simulating rosewood grain.
1937 National Triolian guitar specs:
Rosewood or "Red bean" fingerboard.
1938 National Triolian guitar specs:
Pickguard added (sometimes black, sometimes wood grain with diagonal stripes).
National Triolian guitar discontinued 1938, replaced by the Collegian.