The "Martini" style practice organ was developed by Grigg Fountain, Fenner Douglass, and Walter Holtkamp in Douglass' apartment in 1949. They wanted to design a practice instrument that offered both quick response, and clear tone. The Martini fits under a 12' ceiling under most configurations. Since its invention, the Holtkamp Organ Company has made many more of these instruments, which can be found in the practice rooms of many of the leading organ programs in the United States. For those wondering, the name comes from the cocktail that its creators were enjoying while designing the instrument.
The Martini was designed to be simple and accessible. All of the pipes can be plainly seen in open air, and the pipes are set linearly from bass to treble, not split into C and Cx sides. The bass octave of flutes sits on an offset chest next to the case to account for their height.
The case of Martini is well organized on the inside. The windchests can be seen above, along with its magnets on the bottom. The reservoir sits to the right, above a box containing the blower, and nearly all of the wiring for the organ sits immediately behind the keyboards. There is obviously little room for a person within the case, but individual panels on the sides can be removed for ease of maintenance.
The reservoir sits above a grey box holding the blower in the center of the case. There is a Schwimmer Regulator situated at each side of the reservoir. The smaller windline goes straight into windchest which feeds the bass offset.
The Schwimmer Regulator was a 19th Century invention that allowed windchests to accomodate changing wind pressures. The regulator basically is a movable airtight cover which has springs that accomodate changing wind pressures by adjusting the volume of the space.
The box on which the reservoir sits houses the blower. It serves a dual purpose of allowing the case to be smaller by letting the reservoir sit on top of the blower, and soundproofing the blower. There is a label printed on all sides of the box warning that the box contains asbestos fibers. Although asbestos has proven to be an extremely harmful chemical, it has also been extremely useful in the past for insulation, fireproofing, and soundproofing. Prolonged contact with asbestos dust will cause cancer and other diseases, but short episodes of exposure to low amounts of asbestos is not dangerous. In the Martini's case, it's contained within the blower box so the organist is under no danger, and a single exposure to the asbestos would still be relatively safe for anybody repairing the blower.
Because the various components of the organ run on DC power, and electrical outlets in the United States provide AC power, most organs (except some mechanical action instruments) require a DC rectifier which runs on AC power and provides 10-30 v. DC power. Some organs need more than one rectifier because some components require more or less power.
Below, one can see the stop rail and the keydesk for the Holtkamp Martini. The keys are adjusted to create the illusion that the organist is fighting against 3 inches of wind pressure. Looking at the rank list (which can be found here), one can see that while the Martini is a unit organ, it draws less heavily from each of its ranks than the Möller Artistes.