From james_eaton@btopenworld.com Sun Jan 15 01:45:28 2012
Subject:Re: To change caps in tone generator or not?

Hammond tonewheel generators used wax capacitors ("caps") in the tuned
circuits up to around '64. In some climates, their value increases with
time upsetting the tuning of these circuits.



Capacitors are used on generator tones 49 up to 91.



Larger capacitors are used on tones 49-54 than on tones 55 and up and their
increase in value with time affects the output less but nonetheless has an
effect, so this transition may mask a change in output from the generator.



It is straightforward to tell whether you need to change them,



Tone 48 is the 4th B up from the bottom of the keyboard or B4 on the 16'
drawbar.

Tone 49 is the 5th C up from the bottom of the keyboard or C5 on the 16'
drawbar.

Tone 54 is the 5th F up from the bottom of the keyboard or F5 on the 16'
drawbar.

Tone 55 is the 5th F# up from the bottom of the keyboard or F#5 on the 16'
drawbar.



Pull the 16' drawbar out, push all the others in and turn off vibrato
percussion and any leslie effect etc.



Play a few notes up to the B and then a few notes above it from the C. Is
there is a noticeable drop in level between the levels up to B4 and the
levels from C5 and above?



Play a few notes up to B4 and then from F#5 and above. Is there a
noticeable drop in level?



If there is a noticeable drop in level, your capacitors need changing and no
amount of preamp, amplifier Leslie etc rebuilding can fix it. Sorry for the
bad news!



PS: If you want to confirm, put a voltmeter on the generator terminals and
measure the AC voltage in mV. It should be around 4 to 4.5mV at tones
49-55. You'll probably have about 3mV from 49 and up and then about 1mV
from tone 55 in wax cap organ because of the ageing of the caps.





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