During the total production run of Hammond tonewheel organs, there were several changes made in the number of outputs from the ToneGenerator. This depended on the model and the year the organ was built:
The organ described in LaurensHammonds patent application was never marketed and existed in prototype form only. The tone generator illustrated in the patent had 84 frequencies:
12 tonewheels of 2 teeth 12 tonewheels of 4 teeth 12 tonewheels of 8 teeth 12 tonewheels of 16 teeth 12 tonewheels of 32 teeth 12 tonewheels of 64 teeth 12 tonewheels of 128 teeth
Note that in the patent, there are no tones above the sixth octave like there are in the production organs. The reason is because the hobbing machine used to cut the sinusoidal "teeth" in the tonewheels could not cut 256 teeth. After the patent was issued and before production began, Hammond figured out that a top half octave could be generated with tonewheels cut to 192 teeth and the GearRatio between the DrivingGears and the DrivenGears dropped to that a fifth below the desired pitch. In other words, the gear ratio for the upper C was the same as that used on the F tonewheels below it.
The upper seven pitches are slightly flatter than the other octaves (except F# which is slightly sharper) because of the different gear ratios (another reason a tonewheel generator sounds different than most clones with perfectly divided digital octaves). Unfortunately only seven tones could be produced using these gear ratios so most generators produce 91 tones. But, because of the way the tone generator was designed, the number of tonewheels in a generator had to be divisible by 12. So five blank tonewheels with no teeth (and no magnetic pickups) were used to keep everything running smoothly.
The following models have a 91 frequency generator.
Model A: # 1 - # 2,676
Model B: # 4,000 - #10,549
Model C: # 1 - # 1,247
Model D: # 1 - # 3,143
Model E: # 8,000 - # 8,663
Player : # 9,000 - # 9,209
All 91 frequency models have:
12 tonewheels of 2 teeth
12 tonewheels of 4 teeth
12 tonewheels of 8 teeth
12 tonewheels of 16 teeth
12 tonewheels of 32 teeth
12 tonewheels of 64 teeth
12 tonewheels of 128 teeth
7 tonewheels of 192 teeth
5 blank tonewheels
In an effort to trim costs during WWII, Hammond reduced, for a time, the number of tonewheels from 91 to 82. The 82 frequency generators eliminated the lowest 9 tonewheels and the organs were rewired to accomodate these missing tones. Hammond used a technique common to pipe organs which produce bass tones lower than the longest available pipe by simultaneously playing two pipes tuned a perfect fifth apart. This produces a resultant frequency an octave lower. By rewiring the organ to play a tonic and its fifth at the same time, a resulting frequency an octave lower was produced. However, this has a negative impact on the quality of the tone. Hammonds do not have perfect fifths and this further limited the quality of the tone. All of the 82 frequency models will be quite old and probably not too common. The folowing models have an 82 frequency generator:
Model A: # 2,677 - # 2,711
Model B: #10,550 - #17,074
Model C: # 1,248 - #17,074
Model D: # 3,144 - #17,074
Model E: # 8,664 - # 8,739
Model G: # 4,101 - # 7,349
Player: # 9,210 - only
All 82 frequency generators have:
9 blank tonewheels
3 tonewheels of 2 teeth
12 tonewheels of 4 teeth
12 tonewheels of 8 teeth
12 tonewheels of 16 teeth
12 tonewheels of 32 teeth
12 tonewheels of 64 teeth
12 tonewheels of 128 teeth
7 tonewheels of 192 teeth
5 blank tonewheels
After WWII, Hammond returned to the 91 frequency generators and added ComplexToneWheels to the lowest octave that provided additional odd hamonics to the fundamental. This improved the sound of the bass pedals. The following models have 91 frequency generators with complex tone wheels on lowest octave:
Model BV: #17,075 - #29,737 Model CV: #17,075 - #30,287 Model RT: # 1,001 - # 1,201 Model B2: #35,000 - #40,303 Model C2: #35,001 - #40,459 Model RT2 # 1,300 - # 2,150
The M series SpinetOrgans use an 86 frequency generator. Since the lower manual ends at F instead of C, generators 13(C) through 17 (E) are not needed. Tonewheels 13 through 17 are "blanks" (i.e. perfectly round) and the pickup magnets are missing. Early M organs use the "wide" generator (but unlike the other organs with the "wide" generator, the output terminals are not in consecutive order) and later M, M2 and M3 organs used the narrow generator:
12 tonewheels of 2 teeth (ComplexToneWheels but different in shape and harmonic content than the other organs) 7 tonewheels of 4 teeth (Tonewheels for generators 13 through 17 are blank with no pickups) 5 blank tonewheels 12 tonewheels of 8 teeth 12 tonewheels of 16 teeth 12 tonewheels of 32 teeth 12 tonewheels of 64 teeth 12 tonewheels of 128 teeth 7 tonewheels of 192 teeth 5 blank tonewheels
A short time before the introduction of the 3 series, Hammond redesigned the tone generator to be narrower. These generators can NOT be used to replace the 91 frequency generator above because of differences in the output terminals. The following models have 91 frequency generators in a narrower frame (note that all B3's have the narrow generator):
Model B2: #40,304 - through B3 to end of production Model C2: #40,460 - through C3 to end of production Model M3: #??,??? - through end of production Model RT2 # 2,151 - to end of production
Used in later console organs such as the H-100 and X-77.
See ChorusGenerator
For an in-depth description of the different kinds of tone generators and how they are connected to the manual key switches: 
http://www.dairiki.org/hammond/wiring/
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