Fixing intonation on a resonator

[EdtheSquid]

Hi all,

I've got one of those Johnson reso-mandos. I've been trying to play it lately up the neck out of the first position. I had my tuner clipped on and found that in-between the third and twelfth frets, notes were tending to be sharpish. My Washburn has a compensated bridge and in reading some threads got to thinkin' about compensating the biscuit bridge on the Johnson.

Is there enough material (width wise) on the biscuit bridge to make it work? I thought about laminating some maple on to the sides to thicken it, but don't know if that would be too much. Will it ever be possible to have a proper intonation on that mando?

Look forward to some insight.

thanx,

Ed

[jim simpson]

I believe you can intonate correctly with a replacement bridge. I used to own an old National. I took a solid piece of wood (a scrap of something as I used to turn wood) and made a new biscuit. I would suggest making a new compensated bridge/biscuit assembly to experiment with. It doesn't have to be one-piece, just make a dado cut in the biscuit/disc and glue the bridge material in the slot. Of course you'll want to have enough material in your compensated bridge for adjustments.

[Paul Hostetter]

This is tough. The normal saddle in the biscuit is not really wide enough to do a full compensation. You change the position of the saddle in the biscuit at some peril, because the cone is engineered to take pressure from the strings in the center. If the pressure is too lopsided because you've moved the saddle off-center, the cone may collapse.

On the mandolins I make a new biscuit usually from redwood, mahogany, or spruce. Better (lighter and more resonant) than maple. The best saddle material is a light wood, not bone. Not even ebony. John Dopyera (who invented these things and tinkered with them all his long life) preferred grapefruit wood! I've had good luck with light maple, madrone and a few other similar light hardwoods. If you make a new biscuit and saddle with overall lightness in mind, you can hopefully dial in the intonation in the process.

In some resophonics I've built, I planned the fingerboard location for a standard 5/32" saddle in the biscuit with the whole cone rotated so it's on an angle. You can't usually do this to old Nationals because the center of the cone/saddle is already too close, meaning the string is too short for the fret scale, and rotating the cone therefore makes the intonation even worse. Maybe you get the low G to intonate, but the E will be worse than ever.

One other thing worth exploring is whether you can shift the entire cone back in the well, lengthening the string length in the process. Sometimes that is possible and helps a lot.

I'm not sure which you might have, but Johnsons had some interesting cones for awhile. The good ones (made in Slovakia or the Czech Republic if I remember right) had an elaborate embossed spiral. Replacing the entire biscuit and saddle brought them to life in a nice way.