https://peertube.dngr.us/videos/watch/8b40cd9b-4f2b-4d41-8a5b-211e4118d39c Join us on Patreon. Visit https://www.patreon.com/PeriscopeFilm Part 2: https://youtu.be/zhse34G33A4 "The Step by Step Switch 197 Type Selectors" was made by Audio Productions in 1951 for the Bell System. The film explains the operation of an electrical switch in a telephone system, focusing on the role of various relays (A, B, C, D, E) and mechanical components (shaft, wipers, ratchets, magnets). It describes how these elements work together to connect a customer's call, detailing the step-by-step process of dialing, circuit completion, and signal transmission to ensure accurate and efficient telephone service. • 0:29 - 0:46: Introduction to the circuit schematic and simplified drawing for understanding the selector circuit. • 0:49 - 1:04: Explanation of the relays (A, B, C, D, E) and the mechanical components (shaft, wipers, ratchets, magnets). • 1:25 - 1:43: Description of the customer's telephone and the line finder connecting to the first selector. • 1:54 - 2:01: Simplified drawing showing the dial connected directly to the selector. • 2:10 - 2:26: Circuit completion through the station instrument, customer hears dial tone, and A relay operates. • 2:29 - 2:49: B relay operates, preparing the circuit for C relay and vertical magnet. • 2:54 - 3:08: Customer dials digit three, causing the selector to operate. • 3:19 - 3:42: A relay releases, B relay remains operated, and vertical magnet and C relay operate. • 3:53 - 4:01: Vertical magnet raises the shaft one step, closing vertical off-normal contacts. • 4:19 - 4:32: E relay operates, holding the circuit. • 4:57 - 5:04: A relay operates again, opening the circuit through C relay and vertical magnet. • 5:38 - 5:54: Vertical magnet re-operates, raising the shaft another step. • 6:39 - 6:45: Vertical magnet operates as the dial returns to normal. • 7:02 - 7:07: Customer dialed three, shaft steps up three levels. • 7:16 - 7:27: Selector completes rotary operation automatically. • 7:36 - 7:49: Rotary magnet operates, rotating the shaft one step. • 8:01 - 8:08: Rotary interruptor contacts open, releasing E relay. • 8:24 - 8:30: D relay operates, extending the talking path to the next switch. • 9:00 - 9:07: D relay remains operated until the customer hangs up. • 10:13 - 10:26: Customer dials digit three, A relay releases, vertical magnet and C relay operate. • 10:32 - 10:38: Vertical magnet moves the shaft up one step. • 11:06 - 11:17: A relay operates, vertical magnet releases. • 12:18 - 12:24: Vertical magnet steps the shaft up another step. • 12:35 - 12:47: A relay operates, vertical magnet releases. • 13:00 - 13:05: Rotary magnet is energized, rotating the shaft one step. • 13:27 - 13:31: Rotary magnet releases, E relay and D relay are energized. • 14:04 - 14:09: Next switch places ground on the sleeve terminal, holding D relay operated. • 14:30 - 14:39: Rotary magnet steps the shaft to the next terminal if the first trunk is busy. • 15:00 - 15:04: Rotary magnet opens the circuit to E relay, releasing it. • 15:18 - 15:24: Rotary magnet steps the shaft to the next terminal if the second trunk is idle. • 16:02 - 16:06: Rotary magnet steps the shaft to the next terminal if the second trunk is busy. • 16:19 - 16:23: Rotary magnet steps the shaft to the next terminal if the third trunk is idle. • 17:01: Selector is connected to the linefinder, assuming the first two trunks are busy. • 17:32: Customer dials digit three, shaft steps up. • 18:15: Vertical magnet releases, dial contacts open again. • 19:06 : Vertical magnet steps the shaft again, dial returns to normal. • 19:37 : Vertical magnet releases, vertical stepping is complete. • 20:01: E relay releases, rotary magnet releases. • 20:23: Rotary magnet steps the shaft to the second trunk. • 21:01: E relay releases, rotary magnet releases. • 21:16: D relay operates, extending the talking path to the next switch. • 21:39 - 21:42: Switch steps up to the third level, cutting into the third terminal which was idle. • 21:47 - 21:56: Basic operation of step-by-step equipment, highlighting the rhythm of electrical and mechanical operations. 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