I own a 1970 F212 and it has that jangly sound you describe, and I found that the treble strings (the octave G and D) were slightly out of balance with the corresponding wound G and D, so much so that I decided to change the whole string layout completly.
Before I get into that, I might mention that on a couple of my other Guilds, I wanted to shape the sound of the bottom E string differently, and I tried different out-of-gauge strings to compensate. One, my F-30R had too much bass, if you can believe that, and I tried a lighter gauge string. No effect.
Same thing with my Corona built F-47RCE, only in the opposite direction. That one had very little bass on the E string. Tried a larger gauge. Same thing, no change. Each of the guitars still kept their original personality.
So . . . back to the 12 string. After much research and experimentation, I change my F212 12-string into a
10-string!
Now, it sounds great! More like a six string on a chorus. The first four strings are now in unison, and tuned just slightly out of tune from each other. That give the guitar a built in chorus sound. The remaining strings - A and E - are left as single strings; I removed the high octave strings from them.
I also had to make a new nut, but that was no problem. If you go this route, then I suggest going to a local guitar repairman or luthier, have him do the work for you.
In addition, you will have to buy a custom set, which can get expensive, but the sound you get is worth it!
Here are a couple of clips of me playing this wonderful instrument:
http://www.youtube.com/watch?v=g0Sm0N--UOY
http://www.youtube.com/watch?v=L_DRHhuG ... re=related
Hope this helps!
Metalman - I'm back!