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The zinc plating on the steel components of Hammond organs sometimes can grow metallic fur or dendrites. I have no idea what the actual growth mechanism is (if you know, please enlighten us!). Heat and humidity can tend to speed the growth of dendrites.

Even scientists don't know the actual reasons for dendrite growth. The gravity induced convection makes it impossible to track the dendrite growth. Therefore they made an experiment, that flew with the space shuttle: Isothermal Dendritic Growth Experiment (IDGE). One thing is known for sure: the solidified zinc surface shows the dendrite structure already. And the fresh zinc surface is chemically active. If humidity is high, a zinc solute can occur, which leads to the growth. A way out of this is to plate the surfaces with chrome to passify the zinc. A simple lacquer layer does the same.

Other pure metals (and some alloys) can also grow whiskers. NASA has some good on-line resources on tin whiskers and many other kinds of whiskers. There is some concern in the electronics industry that the elimination of lead from solder --- motivated by environmental and health concerns --- which is currently underway will lead to problems due to the growth "tin whiskers" in all kinds of electronic equipment.

In any case, the dendrites, being metallic and therefore conductive can cause all kinds of mischief in your organ. Dendrites are often the cause problems in the vibrato Scanner, and the Vibrato switch assembly, where they cause MotorBoating, or choppy vibrato; and also in ?PercussionSwitchAssembly, and in the manuals, where they can cause the Percussion to misbehave, or can cause strange hums, funny cross-talk like sounds and other wierd symptoms. Dendrites can also grow in/on the swell capacitor (where they'll cause terrible noises.)


Many people claim they have successfully cured dendrite problems in all of these places by "zapping" --- putting enough current through the little whiskers to burn them out.

Some people advocate the careful use of reasonably low voltages (e.g. nine volt "transistor radio" batteries) to zap dendrites, while others swear by using the B+ supply (a few hundred (!) volts) as a source of zap.

WARNING: Zapping can clearly be hazardous to the health of you organ. Please make sure you understand what you are doing, and appreciate the possible consequences before you attempt it.

I, personally, am extremely leary of zapping. I have used the nine volt battery approach to cure percussion problems which were caused by short in the upper manual. In my experience this is a temporary fix. The shorts tend to recur (usually after moving the organ).

Also, see ManualZapping.

Clearly the ideal fix for dendrite problems is to open up whatever component has the dendrites a clean them out. (Compressed air, shop-vacs, and sticks covered with double-stick carpet tape have all been recommend as useful tools for this task.)

See also HowToRebuildTheVibratoScanner

(Human) Health Issues

Reportedly, cadmium and/or cadmium oxide is highly toxic and/or carcinogenic. Fortunately, however, the concensus seems to be that the whiskers which grow in Hammond organs are zinc, not cadmium. I'm not 100% certain about any of this though, so you might want to be careful around that fuzz. (If you know something more, add it here, please!)

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