Anatomy of a WurliTzer Theatre Pipe Organ

Relay.

Disassembly.

A Wurlitzer Relay needs to be disassembled in the right order! First remove the front glass windows and put them out of the way in a safe place. The cover can be removed from the primary magnet/valve box on the back of the relay. The sealing clamp blocks can be removed from around the cables at the end of the chest. If you are planning to completely rewire the relay you can now chop through the cables and make everything else a lot easier, however I wanted to preserve the existing wiring so I left the cables in place and worked around them.

Next remove the air manifold box from the end of the relay. This hides some screws that you will be looking for later!

Remove the screws holding the relay pneumatic trays. These are found from the back of the relay. There are three rows of screws. One row is just above the bottom of the back board. One is just above the primary box and the other is inside the primary box, but you can get to those screws between the magnets and the valves.

Once all the pneumatic tray screws are out it is possible to pivot the trays out of the chest, limited by the cable at one end. There may be some resistance due to the gasket becoming welded to the chest but gentle persuasion should overcome that. Taking each tray in turn, preferably from the bottom, ease the tray out so you can access the screws holding the contact rail to the tray. With the contact rail separated the pneumatic tray can be removed and the contact rail placed back into the chest. Starting from the bottom means you do not have to hold the top rail up while you work on the tray below.

With the relay pneumatics out the way it is possible to remove the primary box. Most of the screws are from the inside behind where the relay trays were but there is also one in each end, as was found when the manifold was removed. The inside screws are now relatively accessible but the contact rails still need to be negotiated carefully with the screwdriver. Having removed all the screws the box is unlikely to move easily as, again, the gaskets have probably welded themselves to the chest. The seal around the air inlet hole will also need to be broken and removed before you try and remove the box. More gentle persuasion should get the box to move but it is still likely to be a tight fit between the ends.

With the primary box removed it will be possible to see why it is not a good idea to try and remove the whole back board with the primary box still attached. There is a screw in each end of the back board hidden behind the primary box. It is likely that there is a gasket stuck across each end of the chest including the ends of the back board. This makes it difficult to remove the back board but with determination and a long thin blade it is possible to split that gasket away and get the back board off.

After removing the back board it should be possible to remove the top from the top chest and the bottom from the bottom chest but there is no way to get the centre top and bottoms out unless the cables have been removed, which means you cannot replace the gaskets. The top and bottom are also likely to have been gasketed over at the ends and be reluctant to leave.

This is about as far as you can reduce the chest unless you cut the cables.

All the smaller parts, pneumatics, valves etc can then be stripped ready for rebuilding in the usual way.

Rebuilding.

There is nothing very unusual about rebuilding the relay parts compared to any other chest in the organ.

The secondary pneumatics are a different shape to other parts of the instrument so a separate leathering jig was made. As there are relatively few of these to do a simple construction was adequate.

The secondary pneumatics are different from other examples I have seen in the way the contact chopper bar was mounted. On other relays, including the preset relay in this instrument, the bar is soldered to two pins which are pushed into the front edge of the top of the pneumatic. In this case the bar is soldered onto 1/4" wide brass strips which are screwed to the top of the pneumatic. When the pneumatics were cleaned off about half of them had holes drilled to take the pins and the others did not. This may have been a change over point in the production line or an experiment.

Reassembling

As usual it is mainly a matter of doing everything in reverse of the disassembly process.

Assemble the primary box with its pneumatics and valves first and attach it to the back board which has already been replaced on the chest.

Before reassembly I cleaned all the contact bars and the contacts. The bars were first lightly rubbed with fine steel wool then treated with "Deoxit" and "ProGold" chemical contact cleaner. The contact wires were only treated chemically. With a support (ball point pen) held under the contacts they were wiped a few times with the chemically impregnated wipes. It is unlikely you will get the contacts making at the same point they were before so a clean start should ensure they will work first time and then the design will ensure the wiping action will keep them clean if they are used occasionally.

One critical operation that you do not have on other chests is aligning the chopper bars on the relay pneumatics with their contacts. I first glued the gaskets for the pneumatics to the trays. This makes it easy to ensure the holes in the pneumatics are exactly over the holes in the wood. With the gaskets in place they clearly mark the location of the pneumatics so I glued the pneumatics precisely onto the gaskets. When I placed the tray into the chest and attached the contact rail many of the chopper bars were missing the contacts at one end or the other. This was fixed by unsoldering the bars from the brass strip, at one end, warming the other end until the bar could be slid to the correct position and resoldering the other end.

The other relay I attached the contact rail to the pneumatic trays first and glued the pneumatics over the gaskets with a little adjustment to match it to the contacts. Much easier. It will get a little awkward in the corner at the cable end of the chest where you cannot move the tray out far enough for easy access but it will still be easier that realigning all the chopper bars afterwards.

As each tray was completed it is the easiest time to adjust the movement of the pneumatics. First, before fitting the up-stop rail, set the downward limit stop. This is set by the screw in the top of each pneumatic. It needs to be set so that the pneumatic closes far enough to ensure the chopper bar makes contact with all the contacts, with a little extra movement to give the wipe action between the bar and the contacts. This is also a good time to ensure the bar is parallel to the contacts so there is simultaneous contact across all the contacts. Too little movement and the contacts will not close. Too much movement will cause excessive wear on the contacts, fatigue and broken contacts as the wires flex, and an increase in the time it takes the contacts to open after the note is released.

With all the down stops adjusted the up-stop bar can be positioned. This has the buffers on screwed rods that the pneumatics rest against in their open state. These need to be adjusted to ensure all the contacts are open when the pneumatic is up. The one contact on each block that is connected to the power feed should be set slightly higher than the others so that it makes contact first. It is acceptable for the power contacts to remain in contact with the chopper bar in the up position but all the other contacts must clear. Too much free space increases the time between when the note is played and when the contacts close so the instrument reacts more slowly. There must be enough space to be sure all contacts clear but no more.

Properly adjusted the relay is remarkably fast and responsive.

I left the top off the to relay chest until after the pneumatics were installed and adjusted. Makes it a lot easier to work on it. Unfortunately that is not possible for the lower chests.

After everything is adjusted the relay trays can be screwed into place. The primary box cover can then be put on, the front windows put on, after cleaning the glass, and then the manifold box and ventils reassembled. Finally, when all the relays have been completed, the blocks that seal and clamp the cables should go back in place.

One manual relay (the Accomp) took 14.5 hours to disassemble, including stripping the valves and all leather from the pneumatics and gaskets. Releathering, contact cleaning, assembling and adjusting took about 55 hours. In between I did about 55 hours of wood refinishing, but most people would not go to that much effort.

NEXT==>Manual Chest

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