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Calculating Soundbox Volume

Calculating Soundbox Volume

by Dave Raley

Originally published in American Lutherie #70, 2002 and Big Red Book of American Lutherie Volume Six, 2013



Want to design a new guitar shape and maintain an equal volume of enclosed air by adjusting the height of the sides? Here’s how to calculate volumes. Accuracy is a function of how long you want to spend measuring and calculating.

Consider two bodies: Figs. 1a and 2a. The body in Fig. 1 is 18" on the X axis and 4" on the Z axis. Suppose that you wish to make the body in Fig. 2 have the same volume as the body in Fig. 1 while maintaining the same X axis. Fig. 3 defines the axes regardless of the way the figures are turned.

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Questions: Making Your Own Amp

Questions: Making Your Own Amp

by Dave Raley

Originally published in American Lutherie #73, 2003 and Big Red Book of American Lutherie Volume Seven, 2015

 

Joe Oliver from cyberspace asks:

Do you know of a manufacturer of guitar amp kits? Years ago my father bought me a Heathkit, smug in the knowledge that I would never complete it. I fooled him. I played it through high school and into the local club scene up until 1980 or so; my interests changed and about 1990 I sold it to a friend, who promptly lost it.

Now I’m starting to play again and would like to build a bigger and better amp to go with my handmade bass. Of course, there is no kit maker alive anymore, so I’m kind of stuck. I would settle for a good book that catered to nonelectronic-type people.


Dave Raley of Laurel Hill, North Carolina
responds:

Jim Oliver has rattled the cage of a die-hard tube man. I’ve been building and working on them since the early ’50s. I can furnish him a diagram or two if he wants to make up his own kit, transistor or tube. Transistor amps are much simpler to build for a given output power, but you can feed a tube amp into a reflex baffled speaker or a Klipshorn and get more and smoother loudness from 10w than you would from 100w solid state into a closed baffle. Solid state amps, lacking output transformers, handle the back EMF from open baffles poorly.

My reasons to stick with solid state: finding good tubes and transformers is a challenge; no metal chassis is required; less heat, weight, and fragility.

My reasons to go with tubes: no crossover distortion; most harmonic distortion is odd, that is, less detectable to the ear, and when detected is less annoying; failure usually comes on slowly; brief overloads that would be catastrophic to transistors are likely to go unnoticed by tubes and tubes will often forgive abuse; even nontechnical people can repair tube amps. The tubes are the most likely component to go bad, and you can often tell one is bad by looking at it or swapping it with a known good one.

A good source of used tube amps is old organ tone cabinets, like Conn, Baldwin, or Wurlitzer, which you might be able to get for hauling them away. Forget about Hammond, especially if paired with a mechanical generator organ, or Leslie, as these two are worth more now than when new. —

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Stalking the Wild Pine Rosin

Stalking the Wild Pine Rosin

by Dave Raley

Originally published in American Lutherie #78, 2004



Having read Louis De Grazia’s article “Rosin Varnishes” on p. 167 of The Big Red Book of American Lutherie Volume One, and seeking an undercoat that would not turn cedar red, and also not wishing to breathe the fumes of any of the various synthetics, I set out to buy some rosin stock. Couldn’t find it. Eventually I thought to check out the pines in the yard. Sure enough, not a hundred feet from the porch there were nodules of rosin and rosin-coated bark free for the taking. We are talking about good old pine pitch.

Gathering what I could from three trees, I chipped away some of the excess bark and filled a baby food jar loosely, topped it off with 190-proof ethyl alcohol and crimped aluminum foil over the top with a rubber band. The rosin dissolved in about a week and I began to make test pieces using the same stock the instrument was made of, to wit, cedar shingles. The tincture was darker than I had expected. It didn’t stain the test pieces a lot, but more than I wanted. Gotta have more rosin. A half-hour’s walk in the woods turned up enough mixed stock to overfill a quart baggie. About a third of the pines had at least a trace, and one in ten yielded worthwhile amounts. I had intended to fetch some cedar rosin while I was about it but couldn’t find any. Even the cedar that I had taken a branch off of last fall was clean.

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