The late 1920s usherered in many new and fascinating ideas to capture the imagination and hearts of the new industrial age. To my mind, the National Guitar represents the zenith of that eras accomplishments; the perfect melding of form and function ;the amazing melding of wood and metal to create the worlds loudest guitar.
This union of wood and metal required a unique method of construction more akin to the banjo than the guitar. It is because of these unique methods of construction that virtually all National guitars need to be rebuilt every 60 years or so.
The main focus of this rebuilding focuses on realigning the neck with the body (a neck reset). This realigning achieves two things. First, it places the correct amount of string pressure downwards on to the bridge assembly, whether a 'T piece'(National tricone), a 'biscuit'(single cone National), or a 'spider'(Dobro)to pre-stress and drive the cone. Second, it provides for a better neck to body joint, thus more effectively transmitting the vibrations of the neck to the body.
It is important to understand that it is not just the cone that makes the guitar what it is, but the combination of the body, the neck and the cone. If any of these components are out of alignment the sound suffers. The main culprit in this process is the method with which the neck is held under tension to maintain this alignment. Roughly, the process is this: after the neck is carefully fitted to the body and attached to the top and pan of the guitar, the neck stick that runs through the body needs to be held under tension by what are called posts and pads. These posts and pads were generally made out of cheap unaged wood. The shrinking of these posts over the years from drying out often amounts to a quarter of an inch, leaving no tension to keep the neck in proper alignment. This, combined with the natural shrinkage of the neck wood and the years of misalignment, leave old Nationals a little lackluster, not to mention hard to play. But this is also a gross oversimplification of the process.
So many dynamics come into play. In the other menu items I try to cover each section in more detail. Remember, all resonator guitars are bright and possess the ability to sing like no others. When restored properly they regain these properties and sing once more.