Inside the OSI Strasse Orgel

With a bit of luck, you will never have to open up your OSI Strasse Orgel, but if service is needed the following information may be useful. It is based on a short conversation with Paul Fischer, creator of the organ, and my experiences in performing a minor, but important repair. Based on some details, Paul identified our organ as an early one, and the photos may not match all organs exactly.

All repair work is done from the top and front of the organ.

Step 1.  Remove the organ's top. If you still have the original top brace in place, remove at least one end of that first, then undo the two screws holding the front edge in place and remove the top.

Step 2.  Unplug the electronic unit and set it aside. The same single connector is used with either
the MPV-4000 electronic control unit or the Combo Reader upgrade.

Step 3.  Pull the screws holding the plexiglass panel in place, lift the panel, and disconnect wires connecting the charger to the battery. The details of this connection may vary a bit depending on whether you have an early or late model. Early models used a wall-charger and a small plug on the plastic panel. I understand that on later models the charger was installed in the organ itself and the 110 volt cord plugged into the panel.

Step 4.  Pull the four screws holding the top-front panel in place and remove the top-front.

Step 5.  Pull the three screws holding the lower end of the tube assembly to the bellows-and-lower-pipe assembly. You may also want to remove the upper screws as well.

Step 6.  Remove the leaf spring. CAUTION: Note the slot in which the spring is installed. If you reinstall it in a different place you will change the organ's pressure setting, and may affect the pipe voicing and/or tuning! Loosen the top of the relief valve spring.

Step 7.  Pull the eight screws holding the chest-and-upper-pipe-assembly to the case sides. You can now slide the upper assembly forward or backward to access the lower assembly screws.

The 20 electric solenoid valves are located inside the chest. I have not opened the chest to examine them, but I am certain that they are Reisner 601 valves manufactured by OSI. These are high quality valves designed and constructed for major church and theater pipe organs, and should have a long life. The possible "rebuild" would be replacing the felt disks and their leather faces. Replacements should be readily available for your lifetime.

Step 7.  Loosen the six screws holding the bellows-and-lower-pipe assembly to their mounting strips.

Step 8.  You can now slide the two assemblies out of the front of the case. The two assemblies are connected by the main air duct which is held in place with epoxy, and you should not attempt to break this connection without considerable forethought.


The air supply unit consists of a double acting pumping bellows and a reservoir bellows. The pumping chambers are 9 inches by 15 inches. The reservoir measures 14 inches by 6 inches with about 3 inches of movement. The crank stroke is about 55 mm (2.2 in.)

The pressure relief valve is a metal flap with a turned-up tab. It is mounted on the reservoir, just below the battery mount. When the reservoir is full, the operating tab contacts a ball-bearing roller and opens the valve.

Bottom view of the lower pipes. You can see that the lowest two pipes are paired with short pipes producing overtones, making this a 22-pipe, 20 note organ.

Links to additional OSI Street Organ information:

My main Mechanical Music page