UP4014 US&S Coded Cab Signal System Schematic 1948

            From 1974 to 1980 I was the caretaker for the UP 4014 Big Boy at the Southern California Chapter of the Railway & Locomotive Historical Society (RLHS) at the Los Angeles County Fairgrounds. PLEASE SEE ALL THE PICS IN THE “UP4014 BIG BOY” ALBUM. When the engine was delivered to the RLHS it still had its Union Switch and Signal (US&S) company coded cab signal equipment. 

My brother and I were interested to see if the equipment could be operated. The electronic equipment was located on the front edge of the tender in a compartment on the engineer’s side. As you can imagine in that era it was built like a tank and contained 2 vacuum tubes, a 180 code decoder module (to detect yellow or red aspects) plus an amplifier module. See a picture of the equipment here: flic.kr/p/2rprEBc

I was able to contact USS (by looking up their address in the phone book at the local library and then mailing a letter … no Internet ) and they actually sent me the complete manual which included the attached schematic. It’s actually a very simple design. Just an amplifier to detect a weak signal from the induction bar under the front pilot and then present it to a tuned filter, and if it matched, it would make an indication in the cab. 

My brother & I built up a 32 VDC power supply to power the equipment. We built a 180 code oscillator to simulate the signal that would’ve been picked up by the induction bar, We built a 18 chip TTL controller/simulator that allowed a visitor to the cab to simulate travel down the railroad line with different signals appearing ahead which would be duplicated on the in-cab signal boxes and you would use the engineers acknowledge lever in the cab to confirm the aspect. Failure to do so would cause the in-cab air operated warning whistle mounted on the upper back wall of the cab to blow! We had lots of folks failing to acknowledge so they could just hear the whistle 😀. 

So the entire USS equipment was operating with the exception of the induction pick up bar under the pilot of the locomotive. It was so cool that the two T300 32VDC filament vacuum tubes worked plus the four 32V bulbs in the cab signal boxes. Not sure if we could have found 32 V bulbs if they were burnt out. It was pretty neat that it all worked as it had sat dormant for 18 years. Of

Taken on: October 23, 2025

Tags:

UP 4014

Union Pacific Railroad

RL&HS

Southern California Chapter

Los Angeles Fairgrounds

Big Boy

Union Switch & Signal

US&S

coded cab signal

4014

schematic

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