The Electro Tone PER 200 was an after-market percussion kit for Hammond console and spinet organs manufactured before the 3 series models.
As of May 2016, photographs of the kit may be found here: 
http://www.hammondclub.nl/nl/menu/Hammond/De-Hammond-Encyclopedie/Orgel-Uitbreidingen/Electro-Tone-PER200-Percussion-Unit
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