Back to Basics Telephonically

[Paul Berger (Canada)]

(10-03-2015 02:14 PM)Katie Wasserman Wrote:  

Quote:[quote]
They're not especially common, but hard-wired (non-modular) TT sets are out there. I believe the modular connector was first field trial-ed by the Bell System in the early '70s, and then integrated into the production lines as the decade progressed. I've also seen phones which were half-converted to modular in the field; that is, they still have a hard-wired handset cord, but have been crudely fitted with a modular line cord by way of a small modular jack inside the phone base.

There was a period of time between hardwired phones and modular that MaBell used 4-prong plugs and jacks. Mostly these were used prior to touch-tone phones but early touch-tone phones used them too.

The surface mount version of that 4 prong plug was a 404B and the square plug is a 238B they where very common on DP equipment in the late 70s when I started in the computer service business. I serviced point of sale terminals that used these connectors to plug the terminal into a loop, and if unplugged it would break the loop. The one thing I remember about them is how easily the plug could be knocked out of the jack. On the store systems breaking the loop would take down several stations in the store and lead to people running around franticly trying to find the unplugged terminal. One store even went as far as designing a unit that would automatically bypass a lobe on the loop if it detected it was open or shorted. There was also a version of 404B with a threaded hole in the center and a 238B with a captive screw in the middle to secure the plug in the jack.

Wikipedia claims that the 404/238 dates back to the 1930s.