1937 National Duolian in very good condition.  This is towards the end of the production for California made Nationals.  By 1939 the Duolian was gone and the company had moved to Chicago soon to become Valco. This one has the very cool Duco crystalline finish.  One nice feature of the later version is the radiused hard-wood fingerboard often called red-bean although this one appears to be mahogany.  The original cone is in excellent shape and sounds great.  We gave this guitar the full treatment.  Neck angle adjustment, new biscuit and saddle, repro tuners, replaced a chip in the heel, and most importantly added a square 6106-T6 aluminum tube in the neck for rigidity and strength.  These necks are made from fairly soft big-leaf maple.  Adding a reinforcement to the neck greatly improves bass and volume as well as stability.  The sound is big and loud with all kinds of echo.  Check out the great jazz guitarist Russell Malone playing it in open D here.