Hammond Tone Generator Project - Part 1

Early this year, I acquired a tonewheel generator (TWG) from a Hammond series H organ. The H series was rushed into production to compete with offerings from other organ companies, and suffered reliability problems as a result. Here are some photos :

The Tonewheel Chronicles

This TWG had already been removed from the organ and was headed for the dumpster when I picked it up. I have bolted it to a wooden frame to prevent flexing. The Hammond tonewheels organs were produced from 1935 until 1975. Tones were generated by spinning a toothed steel wheel next to an electromagnet. The wheels rotated at a fixed rate, locked to the speed of the synchronous motor. When operating properly, the TWG never went out of tune. This was an improvement over electronic oscillators, where at least 12 oscillators must be tuned to their appropriate pitches. Here is a more extensive description : http://en.wikipedia.org/wiki/Tonewheel So, what can you do with a TWG from a Hammond organ? First, I needed to test the TWG to make sure that it was operating properly.

Hammond T-595

From Hammond T-595

My new, old Hammond T-595. The previous owner got as far as painting the organ to match the room. Has a built in Leslie. From the symptoms (hum, very low sound), I'm guessing bad capacitors or a bad output transistor.

The Hammond T-500's were the last of the tonewheel organs that Hammond produced. Tonewheels generate sound via spinning metal discs and electromagnets. The drawbar controls allow a specific mix of harmonics in the output.

Amusingly, the T-500 Hammond incorporates circuitry to eliminate the uniqueness, classic, Hammond B3 sound. Forutunately, The modifications to reverse these "improvements" are well documented.