‘Biscuit’ Bridge Reso-phonic style Guitar

This is an Ozark resonator guitar from Korea, late 2000s. It is styled on the classic 1920s National Reso-phonic, complete with etched Hawaiian palm beach scenes front and back. It has a single resonator cone driven at its apex by the strings via a bridge saddle sitting on a biscuit-shaped piece of wood. (‘Dobros’ are also resonator guitars, but in contrast the strings transmit the vibrations to the upper large circumference edge of the resonator cone by means of a ‘spider’ as well as to its raised-up centre apex.) If you can believe it, folksy as they now look and sound, back in the day these were state of the art music technology and really the forerunner of the modern electrically amplified guitar in that they were invented purely to be loud to be heard over the rest of the band and the audience (think of them as having a mechanically driven speaker cone inside), rather than for the resulting characteristic sound. The desirability of their particular tone and character was subsequent, ensuring their continued adoption for roots-orientated music ongoing after electric amplification became the widely available norm.

This one had a serious problem in that the neck had movement relative to the body so that it was completely unable to be strung to pitch, complete with broken pieces rattling around inside. These metal bodied instruments are of unique construction compared to conventional wooden acoustic guitars as the neck does not have a permanent glued set dovetail-type connection to the body, but rather a ‘neck stick’ glued in to and extending from it which runs through from heel to butt, and this is wedged tightly with stilts and shims between the metal body’s top and belly, with locating screws through the fingerboard extension, the rim of the sound well in which the cone sits, and the tail piece. As the neck naturally follows the neck stick line this wedging and the resultant positioning of the neck stick relative to the inside of the body and therefore the cone and bridge is critical to the action possible, and the necessary angle of string break-over required at the bridge saddle to transmit the sound effectively to the cone.

This construction method (much of it also shared with the banjo family) pre-dates the availability of wood/metal-capable epoxy glue technology, but having the metal body hanging off the neck assembly in this way (kind of like the way a helicopter really is hanging off its flying rotor) means it is free to sympathetically vibrate with the resonance of the air inside the body, contributing to the characteristic timbre of these instruments.

Repair consisted of dismantling the cover plate, bridge, biscuit and cone, checking and setting up the alignment (the critical neck/neck stick joint had come apart and had to be re-glued), and making up suitable shims for the stilts supporting the neck stick such that the neck aligned correctly with the bridge saddle sitting on the biscuit and cone assembly. Unlike the original 1920s National guitars however, this one does have the benefit of an adjustable truss rod for neck relief at final set up.

A further issue was that the saddle wasn’t a tight fit in the biscuit, and its profile was too flat to suit the curved fretboard radius of 12″. I made a new saddle from quartersawn maple arched on top to suit; this keeps the strings curvature constant up the fretboard and reduces unwanted noise and unintended notes sounding when playing slide. The biscuit on this was a decent piece of hardwood with the grain running in the proper direction, so it was re-used. These instruments are not usually compensated for precise intonation (and this is obviously anyway less of an issue for a slide guitar), so a simple vertical bridge saddle set in to the biscuit slot is all that is needed. The action was set deliberately high for slide playing, and this is also beneficial for the strings’ break-over angle for optimum volume and tone.

The original plastic nut’s end had cracked off, to the extent there was no longer an adequate low E string slot, so I carved a new bone one to suit a heavy set of strings (16 to 54s) for slide playing. I had to shim the replacement nut with hardwood as the neck’s nut slot had been cut so deeply that even a 10mm tall bone blank wasn’t adequate – the factory action with its 8.5mm nut must have been terribly buzzy, and indeed I found the truss rod was completely slackened off; the strings’ tension pull and resulting neck relief would have been solely defining the available action.

Although at first sight the metal body of these guitars suggests they are relatively bullet-proof, and that bellying of the body shouldn’t be an issue with higher string tensions, collapse of the relatively fragile resonator cone certainly can be. The 9.5″ diameter aluminium cone is the key to the sound of these instruments, and a better quality precision spun replacement compared to the stock pressed out item found on this one is a worthwhile upgrade for improved resilience (and to move the tone from ‘banjo-ish’ to real blues territory). However when using down-tuned open G and D for slide and at this short scale length (24 3/4″) the lower string tension means cone collapse is less of an issue.

The frets on this all had sharp edges on the ends, and fairly rough dressing from the factory, so they were lightly re-dressed, filed and polished to make it more comfortable to play.

Because there was no strap button for the neck, I carefully drilled a locating hole and added one to the heel; this guitar is a ‘thinline’, ie it doesn’t have a full depth body, but even so it weighs 9 lbs, being made out of two pieces of pretty heavy gauge nickel-plated brass soldered together, and tying on a strap at the headstock isn’t really a sensible option.

For directly plugging in to an amp there is a single on-board lipstick-type magnetic neck pickup (measuring only just over 4 k ohms, but I guess anything higher would be feedback city with these guitars), with associated volume and tone controls. The wiring was unsecured and flapping about so I used a few cable clips inside to prevent buzzes, and put shake proof washers on the controls and jack socket so they do have a chance of staying in place on the metal body. The pickup was adjusted for output and balance to suit the higher action height. It doesn’t really transmit any of the clank of the guitar’s acoustic character (so miking is required to amplify that), but it is very chimey, and sweet from its positioning; with some reverb it’s good for Afropop or calypso type sounds.

As set up with highish action and heavy strings, even in open G the guitar is quite difficult to fret and barre, and it makes you realise how strong those blues legends’ hands must have been (though to be fair, back then there just weren’t light gauge strings available). But finger a bottleneck and there is no fret clash, which was the objective, and the greater volume and better tone from the heavy strings is where the instrument needs to be at really.

If you work on one of these guitars, have a box of plasters handy – there are plenty of very sharp edges inside, and the rounded-inwards f-holes particularly, though they do a great job at strengthening the top, seem designed to trap and shred (not that kind of shred Yngwie!) flesh from fingers. Have a few sets of strings available too, I broke more zeroing in the setup for this guitar than I would have believed.

As for its sound, well the late great Gary Moore plays exactly this model acoustically on his cover of the old Son House ‘Sundown’ (from the 2007 album ‘Close As You Get’). And for an original National, you can take your pick from all those old blues guys, through Mark Knopfler more recently, and plenty of others. But for me, Rory Gallagher often used one to fabulous effect on a number of acoustic songs he did – check out “Pistol Slapper Blues” for instance.