@Mark Ollig
From 1960 to 1986, the Leich (pronounced “like”) electromechanical all-relay dial system processed phone calls for the subscribers of the Winsted Telephone Co.
From 1960 to 1986, the Leich (pronounced “like”) electromechanical all-relay dial system processed phone calls for the subscribers of the Winsted Telephone Co.
The main distribution frame (MDF), a two-sided steel frame approximately 15 feet long and 10 feet high, served as the physical connection point between outside telephone line cable pairs (external network) and the Leich call processing switch.
The back side (or vertical side) of the MDF, where the outside cable pairs terminated, contained rows of terminal blocks attached vertically along the full height of the frame.
A terminal block was a rectangular block of insulating Bakelite (the first synthetic plastic), approximately 10 inches wide and seven inches deep, fitted with rows of metal lugs that provided dedicated, fixed points for soldering telephone jumper wires.
The cable pairs were soldered to the left-hand metal terminal posts (lugs) of a vertical terminal block.
The corresponding right-hand terminal posts were left open, ready to be cross-connected with a jumper wire to the Leich switch when a specific cable pair was assigned to a new subscriber.
All cable pairs were wired through a two-stage protection system to handle two distinct electrical threats.
The primary defense against high-voltage surges was a carbon block protector, also known as a lightning arrester.
It featured a small air gap that would arc during a surge, creating a path to safely divert the dangerous voltage to the office grounding system and protect the Leich switch.
The second stage used a heat coil to guard against “sneak currents,” which are sustained, low-voltage overcurrents too weak to cross the air gap.
Unable to arc across the carbon protector, the current flowed through the coil, melting a solder pellet to release a spring-loaded mechanism that grounded the line and protected the Leich switch.
On the frame’s front side (or horizontal) side, wiring from the various Leich switch circuits was permanently soldered underneath ten horizontal rows of individual terminal blocks spanning the length of MDF.
Dedicated terminal blocks included line finders, hundreds groups, party-line assignments, trunking, and miscellaneous blocks.
We soldered the MDF cross-connections using “jumper wires,” typically 22 AWG or 24 AWG solid copper.
Jumper wires for subscriber lines on the vertical side of the MDF were wired to their assigned terminal block circuits on the horizontal side.
To provision a line, we first used rosin-core solder to connect one end of a jumper wire to the subscriber’s assigned cable pair on the vertical side of the MDF.
This first jumper was run to the horizontal side and connected to the subscriber’s assigned line finder circuit terminal block.
From that same terminal, a second jumper was then run to the connector block associated with the last four digits of the telephone number.
For an assigned number like 485-4111, this second jumper was terminated on the ‘41’ hundreds-group block and soldered to the specific terminal lugs representing ‘11’, completing the physical path to the correct Leich connector circuits.
For multiparty lines, an additional, separate sleeve wire was run from the associated hundreds group to a dedicated terminal block for party-line assignments.
To minimize the risk of short circuits from splattering solder, we placed a heavy canvas apron over the lower terminal blocks.
Today, MDFs use solderless wire wrap terminations.
When a subscriber lifted the handset, it completed a circuit that signaled the Leich switch.
A line finder would then connect the subscriber’s line to the first available link relay, which provided a dial tone.
After the last dialed digits, the call was sent through the Leich switch.
The voice call path activated the movement of thin, gold-dipped metal crosspoint contacts (yes, real gold) to ensure voice-quality consistency.
Leich documentation described them as “bar-type twin contacts of precious metal.”
I recall the sound of the distinctive “buzz” dial tone generated by a vibrating reed interrupter inside a sealed metal container powered by 48 VDC.
We described the dial tone as sounding like “a bee in a can.”
Many of the relay bars featured Sylvania lamps to indicate the status of active switching selector links, which also aided when troubleshooting.
I recall replacing many of those lamps when one burned out.
In 1981, the Winsted Telephone Co. installed dual-tone multifrequency (DTMF) equipment, allowing the Leich switch to decode tones from subscriber touch-tone keypads.
As a separate but related project that same year, the Leich switch’s “bee in a can” dial tone was replaced with a precise, dual-frequency tone (350 Hz and 440 Hz), as specified in the Bell System’s precise tone plan.
In 1986, Winsted Telephone Co. upgraded from its 26-year-old Leich platform with a Northern Telecom DMS-10 digital call-processing switch.
The DMS-10 used pulse code modulation (PCM) and time division multiplexing (TDM), with programming done through a VT-100 terminal.
That same year, we installed a new MDF using 88 Series Terminal Blocks with wire wrap termination – using, you guessed it, a wire wrap tool to securely wrap jumper wires around the metal terminal posts.
I was certified on the DMS-10 and maintained it for many years; I found it to be an excellent voice-switching platform.
Today, Winsted TDS Telecom telephone subscribers use the Metaswitch platform.
The different kinds of systems used through the years.
The Metaswitch is a “softswitch” that employs Voice over Internet Protocol (VoIP) technology.
The voice packets are transmitted with transport layer security (TLS) for signaling and secure real-time transport protocol (SRTP) for voice encryption.
I was certified on the Metaswitch platform and spent eight years working with it prior to my retirement.
Reflecting on my 13 years with the Leich switch, one memory that stands out is giving tours to students from the local Winsted schools.
They were fascinated by the telecommunications equipment, attentively watching and listening to the rhythmic clicking of the relays as they observed the blinking lights of the selector links.
The students paid close attention as we demonstrated how telephone calls were processed, and they especially liked seeing where their phone’s dial tone originated.
Yes, the old Leich Dial System kept the town talking.
