I posted the photo of the back side of the receiver (earpiece) for a Bell System telephone (either 500 or 2500) set. I said that the green blob in my photo (and the ’44A’ metal can in the wikimedia photo below) was used for reducing the volume of loud signals. Well, that’s only slightly correct.
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Well, Dr. Tyson got a few things not quite right. For one, he said that the area code numbers were chosen so that the most *people* would have do dial the least amount of digits. Well, that was just a side benefit. The central office equipment can’t have a dialer for every telephone, so they
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I blogged this a long time ago, but my old blog is gone, so here it is again. I unsoldered a large number of these 600 ohm hybrid transformers from PBX boards. Each transformer has four 600 ohm windings, and is used to interface to the PSTN (telephone central office). Notice that there is a
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