The Leich Dial System kept the town talking: part one

@Mark Ollig


The Leich (pronounced “like”) Dial System was a telephone call switching platform manufactured by Leich Electric Co. during the 1950s and 1960s.

At the core of the Leich Dial System were its relay bars, which its 1959 catalog advertised as a “jacked-in design permitting easy installation, reconfiguration, and maintenance by simply removing or inserting the entire bar into a shelf slot.”

Averaging 22.5 inches in height and 2.5 inches in width, each relay bar weighed between 10 and 15 pounds and contained numerous relays and electrical components on its front side.

The backside contained a central terminal connector with two parallel rows of copper contacts.

This design enabled the relay bar to be inserted directly into, or removed from, a series of corresponding jacks on the shelving bay’s backplane, providing a secure, solderless connection.

Relay bars were configured as hundred-group line finders and connectors, relay links, first, second, and fifth selector switches, fire bars, interoffice trunking circuits, and more.

In 1960, the Winsted Telephone Company installed the Leich TPS (Terminal Per Station) electromechanical voice switch.

My father, John Ollig, his brother Jim, and Kenny Norman from the telephone company, along with Bud Miller from General Telephone and Electronics and three technicians from Automatic Electric, completed the installation.

The Leich switch replaced the Winsted Telephone Company’s 1940s-era Wilcox Electric step-by-step system, which used rotary selectors.

The Leich equipment bays, measuring three feet wide and seven feet, five inches high, were located in the secure dial room of the telephone office, which featured brick walls and a 10-foot ceiling.

Arranged in three 25-foot aisles, the overhead bay interconnected shelving cables were neatly bundled, often sewn together with twine, and supported in racks about six inches above the bay cabinets.

These cables were the physical medium that established a coordinated voice-switching platform.

Each bay shelf had transparent Plexiglas covers in aluminum frames to protect and provide a visual display the relay bars.

The Leich switch housed hundreds of relay bars, with more added over the years as new bays and shelves were installed to support the growing number of telephone subscribers.

The switch processed the dialed digits from rotary telephones at a speed of eight to 12 pulses per second and supported telephone line loop resistances up to 1,200 ohms.

In 1960, the Leich switch used a ringing generator supplying 70 to 106 volts of alternating current (AC) at a frequency of 20 cycles per second, now referred to as hertz (Hz).

During ringing, this AC voltage was superimposed through a cut-through relay to the telephone line and into the subscriber’s telephone.

Winsted Telephone Company equipped all their telephones with single-frequency 20 Hz ringers, and subscribers leased their phones directly from the company.

On a private line, the Leich switch sent the 20 Hz AC ringing voltage across the telephone line’s tip and ring wires to activate the telephone’s ringer.

For a two-party line, however, the switch achieved selective ringing by sending this same 20 Hz AC ringing voltage down either the “tip” or “ring” wire side, activating only the telephone specifically wired to respond to that side.

For four-party lines, the Leich system, combined with specific in-telephone wiring and central office configuration, enabled selective ringing.

This ringing configuration was achieved by creating a “polarized” ringer in each telephone, which involved wiring each phone with an inductor to respond to the 20 Hz ringing frequency and a cold-cathode vacuum tube to verify the ringing voltage’s positive or negative polarity.

The Leich switch leveraged the sleeve lead (single wire) party positions at the main distribution frame to send “divided ringing” (selecting either the tip or ring wire) and apply a specific DC polarity.

This combination generated four unique ringing configurations, ensuring only the intended telephone on the shared line would ring.

On eight or 10-party lines, the Leich system used coded ringing, which involved applying the ringing voltage in a unique pattern of short and long bursts assigned to each subscriber.

The Winsted Telephone Company’s central office battery room contained 24 large lead-acid cells housed in thick, rectangular glass containers known in the industry as battery jars.

Each 150-pound cell contained heavy lead plates immersed in sulfuric acid.

The glass jar provided a stable, non-reactive barrier to safely contain the corrosive acid while also allowing for visual inspection of electrolyte levels.

Wired in series, these 24 cells formed a single battery, with each cell contributing 2.1 to 2.2 volts DC to provide a total voltage of 50.4 to 52.8 volts DC.

The central office power plant used a rectifier to convert commercial AC to DC for powering the Leich switch’s call-processing systems and ancillary devices.

It maintained a 50 to 54 volt DC float charge on the 24-cell battery, ensuring the Leich switch operated within its required 44 to 54 volt DC range.

This float charge ensured that the battery remained fully charged, allowing the Leich switch and connected subscriber telephones to continue operating even during a commercial power outage.

Anyone with a Winsted party line might recall this announcement: “You have dialed a subscriber on your own line; please hang up to allow their telephone to ring. Thank you.”

Leich kept the whole town of Winsted talking.

Next week: part two.