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General Electric Searchlight DEC project completed.

As many of you are aware the Museum has been hosting the Great LA Air Raid for some time now. The event started out with less than 50 people and one searchlight and is now bringing in around 700 people, a tank, vehicles and aircraft flyovers and as many as five searchlights. 3 years ago Mr. Tom Horsfall attended one of the air raid events. Tom is a radio enthusiast, researcher, restorer and operator and has many electronic/ mechanical museum restorations under his belt. Together with other Museum volunteers Tom operated the Museum’s 1942 GE searchlight (its official name is the 352nd Coast Artillery Anti-Aircraft Searchlight Battalion Memorial Searchlight) and was part of our demonstration team. Tom commented to the others that it would be a lot better to demonstrate the light with its Distant Electric Control station or DEC instead of operating it with the manual control arm. Unfortunately the Museum’s light had been modified for commercial use and all of the necessary equipment had been stripped off with all connecting wires cut and the system was basically destroyed.

The DEC system allows the light to be controlled from a distant location. The DEC is a stand alone station connected to the light through a cable. The DEC allows the operator to look through a set of binoculars to acquire the target and then the operator can track the target without being blinded by the light itself. While lights, generators and DECs are still obtainable, it is very difficult to find fully operational sets.

Tom, who lives in Richmond California 400+ miles away from San Pedro, approached the Museum with the idea of restoring the light. He came up with the plan to make monthly 3 day visits to the museum and felt that within one year he could have the system up and running. Previously the museum had been told that it would be virtually impossible to restore the light to its 1942 configuration.

Beginning in January 2009 Tom began making his visits. His first visit was scheduled to conduct an inventory of missing parts and manuals. He steadily acquired the manuals and carefully studied the schematics and learned how the light worked. The next few visits were spent cleaning the light and searching for missing parts. His searches led him from former commercial operator’s junk yards, to military museums and to remote desert boneyards. Throughout the state he travelled acquiring parts and pieces. Wiring looms were especially difficult to obtain because almost all of the parts lights had been stored outside and the rubber insulation had seriously decayed. In other cases the interior wires were tested and had no conductivity. Furthermore, most commercial operators discarded or destroyed the DEC related equipment so not every visit produced results. One of the first major problems came after locating the parts.

The system requires two amplydines and a dynamotor to provide the necessary AC and DC power to run the system. In addition there are multiple internal sylsens (servos) that communicate with the other electronics to effectively operate the system. While he did find many of the parts he discovered disasters with them. The amplydine interiors were damaged and had to be rebuilt. The Dynamotor had been the home for a very large desert ant community and was almost totally worthless and the Selsyn housings were made of a magnesium alloy that had corroded and expanded with the intrusion of moisture resulting in the destruction of delicate interior wiring. So, he had the missing parts, all of which needed complete overhaul and in some cases were beyond resurrection. Tom, through a myriad of contacts located individuals to assist him with the rebuilding of the amplydines and dynamotor and paid for the restoration on behalf of the museum.

He went back to the commercial operators again buying parts personally for the project. He then made yet another trip to a very remote desert boneyard with a one trip collective 1000 miles travel to gain parts. The trip was held up by the selsyns. It seemed that nearly every example from as many as five different lights were damaged beyond repair. Still, through steadfast dedication he was able to find operational units for the operation of both the azimuth and the elevation of the light. About six months into the project he had all of the parts needed but now the real work started; the wiring of the system.

The looms were originally part of an assembly line production. In many cases looms and leads were installed and then other looms for other control systems were installed over the DEC leads or sometimes tied with them. More significantly the commercial operators had simply cut the multi conductor cables with hack saws at the junction boxes in some cases ripped them out. The trick was to figure out the right cables for the right terminal blocks inside the various junction boxes.

Once inside the project was made more complicated by the discovery that some terminal blocks had their numbering system located at the top of each terminal connection point while others had them below the terminal connectors. So after carefully reweaving the looms into place every wire had to be tested once again before work could proceed. Another set of parts that proved difficult to find were the small brushes that ride on the collector rings. There were a few brushes corroded in place on the light that had to be removed and then new brushes with the very delicate springs and wires had to be located.

Craig Michelson of the American Museum of Military History located in Rosemead said that he had some derelict lights in his storage yard and that he would be willing to donate them to the project. These small brushes were carefully installed and we were ready to begin testing. This series of testing lasted until the fall of 2009. With more progress with each passing month Tom brought more and more of the light back into operation.

The first test came with the Azimuth control from the DEC. Tom brought a small portable power supply that simulated the power from the generator for the DEC system. Tom commented “You know if this works first time out it will be a miracle”. The system did not work. First a fuze in the main terminal box failed and then an after market fuze was somehow tied into the main switch box and it had to be removed. Next test, azimuth began to move with DEC control. Staff marveled at Tom’s work but we soon noticed that the light was moving opposite the controller as tom directed it left the light moved right. Unfortunately, this test was on the last day of Tom’s monthly visit so we were in suspense for a month. When Tom return he examined the terminal connections in the selsyn and found that here was a case of the terminal number being on the opposite side of other terminal numbers. So a switch of connection and we hade Azimuth control for the first time. Next came elevation. We doubled checked wiring and prepared for operation. We soon learned first hand, although we knew from stories that commercial operators hated the DECs because they can hurt you. If someone moves the light while the DEC gears are engaged and then puts power to the DEC the light will correct itself to the position determined by the DEC and in a hurry! In our case the light was out about 180 degrees and it made the turn in a couple if seconds. It awesome to see the light work on its own but was also a bit scary. Tom showed us that if you inspect the instruments called “zero readers” on the DEC one can adjust them to the light’s positions and then switch power on the DEC and there will be no movement. But woe bit it to those that forget.. The next problem encountered was the movement of the light was not quite as responsive as we thought it should be. This was determined to be a faulty switch mechanism that Tom discovered during his trouble shooting. We soon had a replacement switch and it seemed to fix the issue. Still there was a stalling of the light in both elevation and azimuth as it rotated. Tom soon traced this problem to dirty and scarred collector rings in the base of the light. Under careful supervision of Tom the rings were cleaned and testing continued.

The light was running smoothly on power from the power supply, it remained to see what would happen when power came from the generator itself and testing proceeded. The first run brought a couple of blown fuzes but these failures were diagnosed by Tom and quickly fixed by replacing them and cleaning the contacts. All of the contacts of this light had been moisture damaged at some point and cleaning them all was paramount. Soon, operation of the DEC was accomplished with the arc burning and we all had a great sense of elation. Tom had done the near impossible task as described by other volunteers. The light was finished and prepped just in time to be used in the 2010 Great Los Angeles Air Raid event held in February 2010. The event was a great success due in large part to the efforts of Tom Horsfall, Our hat is off to you Tom!

Tom is considering additional searchlight restoration projects and would like to help the museum find a Sperry 1941 DEC unit or any related parts. He would also like very much to find a sound locator that was used with the lights so if you or anyone that you know has searchlight related parts please have them contact the Museum at (310) 548-2631.

The restoration of the museums 352nd Coast Artillery Anti-Aircraft Searchlight Battalion Memorial Searchlight has been an ongoing project of the Fort MacArthur Museum for several years now. To learn more about the history behind this project, please visit our restoration projects pages.

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