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.