-- forwarded message, please reply to sender and MMD --

 [ MMDer Dave Goggin asked Mr. DeMajo how cheaply one could
 [ build a small theater organ; the result is this article and
 [ the accompanying photos at the author's web site.
 [
 [ Mr. DeMajo explains:  "I am an engineer who has been involved in
 [ HVAC design for 35 years now.  I got into computers about eight
 [ years ago when I started to realize my days of crawling in hot
 [ attics were growing short.  I have always tinkered with electronics
 [ as a ham radio operator since I was 12 years old.  I am always
 [ looking for ways to simplify designs (the engineer in me), make them
 [ more "electronic" (the ham genes) and make them last longer (I hate
 [ to do maintenance on my toys).  This pretty well states my
 [ philosophy of organ building."
 [
 [ -- Robbie

A couple of years ago, this writer realized a dream of acquiring a
seven rank Wurlitzer organ for our home.  As with most 1920's vintage
instruments that have been in storage, its pipe work was in reasonable
condition but the chest leather was another story.  The entire organ
came on one seven rank chest, which was hard to handle because of the
weight involved.  Additionally, installation was limited to one rather
large chamber.

Since the chest was in need of complete rebuilding we decided to weigh
an alternative plan of building new single rank chests which would be
easier to handle and would allow placement of the organ into two
chambers.  Commercially made chests start at around $2500 plus freight.
At that price an entire organ was well beyond our budget, so "Plan 'B"
was to try our hand at building chests, in the home workshop, at a
projected cost of around seven hundred dollars each.

Having had the benefit of sixty years field testing on Wurlitzer's
original design, there appear to be some subtle modifications one can
make to simplify and perhaps eliminate some of the problem areas for
which Wurlitzer is noted.  One such modification involves adding
Plexiglas windows to the back of the chest as a means of viewing
alignment of the action once the unit was assembled.  Another is the
elimination of Wurlitzer's cumbersome bottom board gasket arrangement
wherein wind channels are passed through detaching wood components.
Finally, a radical departure was a decision to eliminate primary
pneumatics from the design.

About now there are surely a lot of readers cringing; however,
Wurlitzer took this bold move in their later designs, apparently
without degrading the quality of their instruments.  As Doug Powers
reported in an informative writing published last year [ref. 1],
one notable primary-less organ was recorded by Walt Strony in his
"By Request" album and there was no audible difference in the response
of the action even on a fast moving arrangement of "Tico-Tico".

Powers goes on to explain that modern, adjustable orifice chest magnets
allow primary-less theatre organ actions to be set within a range that
will suit almost any music.  If Powers was right in his assumptions,
the cost savings would make it well worth a try so, with the help of my
teen-age daughter who is always looking for new hobbies, we decided to
undertake the construction of a prototype chest for a 73 note Concert
Flute rank.

The first step was to find quality lumber with which to fashion the
chest sides and front.  Visits to several handyman supermarkets proved
disappointing.  We finally located a local lumber yard that specializes
in fine woods and were able to obtain twenty-five board feet of
straight, knot-free poplar for about $130.

Poplar is excellent for organ work and it was material of choice in
original Wurlitzer chests.  A good thickness plane can work wonders in
cleaning up marginal lumber stock and providing the builder with clean,
uniform surfaces with which to work.  Most lumber suppliers will plane
wood for a small fee.  Small planers are available for under $400 and
these represent a very useful addition to any organ builder's tool
collection.  Armed with a 10" table saw, a small router and an electric
drill, we were able to construct the entire chest in about fifty hours
of actual work time.

Our simplified design utilizes pneumatics of the exact type used by
Wurlitzer.  On original instruments we have encountered over the years,
power pneumatics are seldom the cause of failure unless the leather
has deteriorated and torn.  Wurlitzer replica pneumatic blocks are
available from outlets such as Organ Supply Industries or Arndt Organ
Supply [ref. 2], and they can be easily leathered in the field.

Use caution in selecting power pneumatics since size is important.
Reducing the surface area will affect the action's ability to produce
sufficient power for opening of the toe valves.  Wurlitzer's valve
dimensions were carefully calculated, and adhering to the original size
is strongly recommended.

Since we elected to eliminate primary pneumatics, selection of the most
efficient chest magnet became a real concern.  After studying many
catalog cuts and manufacturer spec sheets, we decided to employ Reisner
chest magnets (OSI part # 5501.32) because they are well suited for
higher pressures, feature an adjustable orifice, and operate with 150
ohm coil resistance at 12 volts DC.  This works well with most solid-
state switching relays and the cost is very reasonable (around $5 per
magnet, complete with gasket).

Next, we decided to attempt elimination of the inherent problem
Wurlitzer created when they channeled the pneumatic passages between
the bottom board and the chest side wall.  By making our bottom board
permanently sealed and affixed to the chest side containing the power
pneumatics, we would never again have to fight with leaking gaskets.
Access to the chest is through a removable back panel so the airways
become part of an integral sealed unit that should never require
maintenance or disassembly.

Our prototype is such that the air passages make a right angle turn at
the junction of the bottom and side.  Someone later suggested mounting
the magnets on the same surface as the power pneumatics.  An excellent
idea, provided the height of the chest is increased by two inches.  The
magnets require two openings: one for the coil to penetrate into the
wind box, and one corresponding to the entrance to the air channel
leading to the pneumatic bellows.  Use of an edge-drilling jig proved
essential in centering the half-inch air channel borings in the chest
sides.

When voltage is applied to the coil of the chest magnet, a ferrous disk
valve lifts and causes the leather pneumatic to vent to atmosphere and
collapse.  This causes the tab at the end of the bellows to press on a
metal spoon rod which, in turn, opens a flapper which admits air to the
pipe.

There were several sizes of pneumatics used by Wurlitzer.  A complete
listing of these dimensions are available on the web site of the
S.M.G.C. Chapter of A.T.O.S.  The web address appears at the end of
this article.

While our project employed surplus original Wurlitzer toe boards, new
toe boards can be easily constructed with the same tools applied to
construct the chest housing.  For those who are faced with fabricating
the toe board, replica Wurlitzer flappers, guide pins and spoon rods
are also available through the outlets mentioned herein.

Our final exterior dimensions worked out to be 7'4" long x 12" high x
10" wide.  Checking the accompanying photos (on the web site which we
set up to supplement this article) will give the reader a better idea
of shapes and sizes of various components.  Our stock for the chest
side, where the pneumatics are glued, measured 1-1/4" x 8".  We would
suggest that if the reader chooses to place the magnets on the same
surface as the pneumatics, a 1-1/2" x 10" x 8' poplar board would be
appropriate for this member.

Looking at the construction drawing available on the web site, you will
note that the air channels exit to the outside of the chest at one side
of the bottom corner.  In placing the magnets on the side board, you
will instead end up with drill hole openings at the top of the chest
side member.  After the drilling is completed, these holes will need to
be plugged.  We addressed this problem by inserting 1/2" wood dowels,
cut to 5/8" lengths, into each hole and gluing them into place to seal
against air leaks.

In the total scheme, there are now only three moving parts per note
as compared to six or more in the original Wurlitzer chest design.  The
troublesome dual disk valve, threaded rod stem, and delicate primary
pneumatic operator are eliminated, as is the bottom board gasket,
spring loaded screws and other miscellaneous instruments of torture
passed down to us by the venerable Mr. Hope-Jones.

To place the final test of Mr. Powers' assumptions, we connected
a keyboard to the chest and proceeded to rattle off an Ethel Smith
arrangement of "Tico-Tico".  At ten inches W.C., the chest performed
flawlessly, even with the factory default adjustment on the magnet
orifices.  Quite a satisfying experience for the author and his
assistant.  The wife was pleased, too, when she learned that the
project came in under budget.

Note: This article runs in conjunction with an accompanying web site
which provides detailed photographs and downloadable construction
plans.  To visit this site on the World Wide Web, please go to

  http://atos.stirlingprop.com/chest/index.htm

We wish to thank the South Mississippi Gold Coast Chapter of the
American Theatre Organ Society for allowing the web portion of this
article to be hosted on their facilities.

John DeMajo
New Orleans, La.

References:

1. "Adjustment of primary-less Wurlitzer chests", by Doug Powers,
   available through the Knowledge Base of the S.M.G.C. Chapter of
   A.T.O.S web site at  http://atos.stirlingprop.com

2. Organ Supply Industries, 2230 West 50th. Street, Erie PA. 16506
   Arndt Organ Supply, P.O. Box 129, Ankeny, Iowa 50021