1957 National 1133 Solidbody 3/4 Resonator Guitar

The 1133 was National's cheapest, student-level resonator guitar (with a roundneck) at the time. It's very short scale at around 22" and has a stubby, fat, round neck shape and 10" (or so) board radius. I've owned one or two and sold another over the years and they're always good fun when they come in. They do have a number of "factory design flaws" that need ironing-out for them to be good players, but once that's done, they're super-fun, take-anywhere guitars that pack thin and small and have good-enough volume to hang in a jam with, even if it's on the thin and banjo-esque side.

This one arrived with a customer of ours and wound-up getting a level/dress of the frets (thanks, Sarah) and then a lot of glorified setup and modification/tweaking done by myself to both make it more stable and functional. Said modifications and descriptions can be found way down lower in this post. It's a good player, now, and I was very tempted by it.

OK, now on to the repair side of this instrument...

First of all, this giant hole in the middle and an actual lower sound chamber with a no-center-hole vented coverplate for the rear is why these small-cone, '50s Nationals sound acoustically a lot better than most modern-day solidbody resonator guitars. It's vented!

Here's the smallish (8"?) cone sitting in the soundwell.

Here's the cone after I had to trim one edge to allow it to get into proper position for good intonation at the saddle. I'm using aluminum tape strips to keep the cone exactly where I want it, so if someone takes off all the strings, it won't move-around out of position.

If you're thinking that I'm hurting tone with these alterations -- no -- the cone is acoustically not very active beyond the "inner hinge crimp" thingy, for the most part. That crimp area just allows the cone to "spring" up and down like a speaker cone, while almost all of the sound is generated in the... conical... part of the cone!

Note that I've also compensated the saddle, here, and lightly glued the bridge on top of the cone in place so it can't swivel around on its mounting screw inside.

So -- the next problem is a big design flaw on these models. The factory saddle design is a good height for the strings over the coverplate but the back-angle from the tailpiece over the bridge/saddle is awful. This is a combination of not thinking, a domed coverplate that forces the tailpiece up on the body, and the (rather stupid but very hip-looking) classic National tailpiece design which raises-up the strings about 1/4" too far by default.

Here you can see the ideal string-path height the original, unmodded saddle has from the factory.

I am going to preface my next set of suggestions and changes by first saying that I have worked on hundreds of resonators, many of them for gigging guitarists who need them to function correctly. I know what works and I know what fails on the road or even in the back of a car on the way to a jam. Resonator guitars mostly use historic designs that are not always good and benefit from improvements. 

Resonator fascists will tell you that under-stringing the tailpiece like in the above photo is evil and shows my lack of moral fiber and lack of proper judgment. Here's the thing -- how else are you going to add back-angle behind the saddle in this circumstance?

The guitar was made wrong from the factory. Adding a little height to the saddle (maxing it out under the coverplate rest) would only add about a degree or so of "extra back angle" which is too shallow to even keep the strings nicely locked in-place in the saddle, let alone drive the cone well (and, buddy, the reduced tension on the cone from the very short scale length means that the cone can use that tension).

So, yes, dang it -- I understrung the tailpiece to solve the problem. Every other solution to this problem is more problematic than just doing that. As a bonus, it pulls the tailpiece off the top so you don't need to stick rubber under there to keep it from rattling on the coverplate...

The next design flaw on this instrument is the neck-bolt attachment. In this guitar, the upper bolt tightens the neck to the body (and it's a proper bolt that's threaded into a magnesium rod in the neck's interior). The lower bolt is actual a "micro-tilt" action adjuster -- tighten it to force the neck back and set your action lower or loosen it to set it higher for, ya know, slide work!

The flaw here is that a single-bolt attachment is naturally loosey-goosey and so the neck will swivel and lean from side to side a bit if you only use the factory setup here.

Once I dial-in the neck angle the way I like with the micro-tilt it I simply add a second, lower bolt to the whole design to lock the neck in place. This is closer to the way a Fender neck with micro-tilt works. I think of it as pretty necessary for someone who actually wants to take this out of the house and travel around with it (the ideal use-case).

Last, but not least, most National/Supro guitars from this era have really dumb headstock problems. The tuners sit high enough and the neck has such low back-angle at the headstock that it's necessary to add string trees (like on a Fender) to add back-angle to the nut from the strings. In the above photo you can see the "natural path" of the strings (almost flat from the D&G tuner posts) as compared to the "in the string tree" path which is more even-keeled.

Without solving this problem, these guitars are almost unplayable as the A,D, G, and B strings are usually noisy, often rattly, overtoney, and odd-sounding with too low of a back-angle running behind the nut.