Gibson PB-1 #9663-6
Gibson's 1927 banjo catalog described the PB-1 as "worthy of every confidence, priced for every purpose and guaranteed by Gibson." The PB, or plectrum banjo, is a four-string banjo with the same scale length and tuning as a five-string; it allows for chord melody playing without a fifth string to get in the way. In 1929 the non-Mastertone style 1 made the transition from shoe-and-bracket construction to a one-piece flange; some early one-piece-flange style 1 banjos exhibited other features identical to the later shoe-and-bracket examples, including the "Coke-bottle" peghead shape, silkscreened "The Gibson" peghead logo, dot fingerboard inlays, and resonator with binding on the back edge only.
#9663-6 dates to 1930 (see Gibson banjo serial numbers vs. factory order numbers), making it an unusually late example of a "transitional" style 1. A mixture of neck types has been observed in lot #9663, suggesting that Gibson may have used it as an opportunity to clear out various obsolete components remaining in inventory. This banjo was likely shipped without an armrest and is shown with an aftermarket non-Gibson type installed; some photos, including the one in the upper right, show the banjo with its original Grover "window" or "first model" tailpiece, while others show it with a later replacement.
Photos courtesy of an anonymous owner.