Gibson made a line of banjos' in the early 20's to early 30's, before the full resonator era that featured a flatback, but hinged, resonator.The resonator is in two pieces, hinged together with springs. You can open one half of the resonator and the sound was projected towards the player.They made about 5 models, 5-string, tenor, plectrum, mandolin and uke. The Banjo Uke has a 9" head.The headstock is not uke shaped, but follows the mandolin style of the day and is the 'snake head' shape.The one on the right in the pictures is the older one, verified from the Gibson web site as a "UB" from 1924. I don't yet have a date for the newer one, pictured on the left. The "door" on the back is spring loaded and pops open when a knob is turned, releasing a latch that attaches to the co-ordinator rod inside the banjo.There is a snap that then attaches to the co-ordinator rod to hold the door open. The springs are broken on the older uke, and I have put small brass hinges on the door to keep it from falling off when unlatched. Perhaps you can see the mechanism on the picture of the sides. Also have a close-up of the door and armrest on the newer uke. The differences that I have noticed so far are: Newer uke has grooved tension hoop, different shaped peg head, different tail piece.They both have a mandolin shaped neck, 9" pot, "The Gibson" silk-screened logo, Grover patent tuners, single ply binding on the resonator.This information and photographs on these unusual Banjo Ukuleles was contributed by Stephen Shelton in North Carolina, USA to whom I give my grateful thanks.
More info from Steve SheltonI have finally got an authoritative answer on my trap - door banjos, from none other than George Gruhn himself. I emailed Gibson looking for info and they suggested I email Gruhn Guitars in Nashville and Elderly Instruments in Michigan. I did so, and to my amazement, I got a return answer from George Gruhn himself! Below is a copy of his email.Most notable is his statement "These instruments were catalogued uke-banjos, ... " They pre-date the standard Gibson Uke-banjos, UB-1, U B-2 etc. by at least a year.I emailed the serial numbers and the pictures that I previously sent to you, and in his second email, he verified them as US's and identified both instruments as produced in 1925.YES, I have legitimate Gibson banjo ukes!Steve Shelton
George Gruhn wrote:Info is available in my book "Gruhn's Guide to Vintage Guitars". The chapter on Gibson covers all the banjo models evercatalogued by the company.If you send photos and serial numbers of your instruments I will be happy to identify them. A 14" scale 4 string model withtrap-door resonator and blond finish would be a UB model produced between late 1924 through 1925.These instruments were catalogued uke-banjos, but the neck dimensions are like a mandolin. We usually set them up as 4 string mandolin banjos.The later Gibson uke-banjos have standard uke dimension necks,George Gruhn