This is a Western Electric Teletrainer set—not a very nice example at that. It seems that there isn’t much about these on the internet, so here you go.
From what I have gathered, these were originally provided by the Bell System to teach elementary school children how to use the telephone properly. In any event, it crosses into several of my main areas of interest (WE telephone equipment and vintage educational equipment, namely), so I just absolutely had to have one.
Much more detailed information about these sets can also be found in the BSP 473-411-100 (issue 4, Jan 1974) manual (or, if you are lucky enough to have the key system version of the set, see the BSP 473-411-901-PA (issue 1, Oct 1967) manual).
Here is the Teletrainer set, set-up and powered-on. The 500D telephone sets both have 25ft line cords, and have the appearance of being thrown together out of spare parts (significantly more than sets that I have seen that were issued to normal customers, anyway). Note also that the pink set is not really faded. The plastic (except the dial plate) seems to have been painted beige-ish at some point, and the paint is half worn off (all the parts are real -59 “rose pink”). The “paint” definitely doesn’t feel like the grade of quality that I would expect WE to use, so I don’t know who could have done that.
Here is the front view of the KS-16605, List 1 Teletrainer control unit. The rather basic controls allow the instructor to manually ring either phone, or apply a “dial tone” or “busy signal” to the system. All buttons are push-and-hold. The unit also amplifies the talk line (along with all tones and dial pulses) for the entire class to hear through the speaker.
This is the back of the Teletrainer control unit, showing that it was actually manufactured by Sentinel Electronics Inc. It seems that several companies made these things, including Dukane (I really wish mine was a Dukane, even though it would be almost identical).
I haven’t come up with the male end of that Amphenol connector to test the output properly, but I have rigged it (rather haphazardly) to a low-impedance balanced microphone connection enough to see that it does work. The manual states that it is a high-impedance connection, but doesn’t say what the nominal output level is (it didn’t seem too high with the microphone preamp). I hope to come up with an appropriate plug someday and make a cable for it (the manual refers to the part as a “No. 80PC2F Connector”).
Also note that this chassis uses 548A round four-prong jacks rather than the square ones pictured in the manual (same as in the normal flush-mount jack assemblies in either case, it seems). One of the telephones had a square plug when I got it, so I added the round plug with the logo to the set (the original plugs have no Bell logo on top).
This is the inside of the KS-16606, List 2 telephone set carrying case. Unfortunately, I ended up with two of these and no List 1 control unit case. It seems the place that originally used this set had more than one and the parts got mixed up (I also suspect the pink phone originally belonged to a different set). If anyone out there ended up with two List 1 control unit cases, I’d probably like to trade a phone case for it.
Here is the bottom of the control unit. Not much to see except the trashed schematic. I wonder why they bothered to put that there—wouldn’t anyone who is supposed to be working on one of these have access to the BSPs with schematics?
It seems that this entire thing (case and chassis) is made of aluminum. Note the date stamp of 7-68 on the front. This unit uses a 6AV6 and 6AQ5 amplifier tubes and a 6X4 rectifier. In this example, the original Sentinel branded tubes are still in place. The device on the back-right side is the timer cam that controls the ringing cadence and the busy signal.
This is by far the most immaculately-clean piece of tube equipment I have ever seen (probably due to the carrying case). I don’t see the need to modify it (replace any capacitors) yet—it doesn’t hum or anything. The pristine-looking selenium rectifier (the orange multi-plate device to the middle-right) does worry me a bit, though. Note also that the cadence timer cam assembly is driven by a 10rpm Cramer type 117 synchronous timing motor. (The apparent curve on the front of the chassis is just an optical illusion created by the closeness of the camera; the edge is perfectly straight in real life.)
Here is another view of the timer cam (from right-outside). The finger-switches that control the ring and busy signals are in the back of this picture (note the busy signal cam on top and the ring cadence cam on the bottom of the nylon cam assembly). The microswitch in the front (of this picture) only controls the power to the timing motor. When the ring or busy button is released, the timing motor continues running until the cam is reset, so that the ring signal is always sent immediately as the button is pressed. ((The timer cam assembly is one of my personal favorite parts of this device, hence why I focus on it.))
This unit is capable of providing a ringing signal of 20Hz at 120v (mains voltage) in a two-four cadence (two seconds on, four seconds off, repeat; the US standard) for as long as the ring button is pushed. Because of the slightly higher than normal voltage, this thing will produce noticeably loud rings (and so it is not particularly useful for testing weak ringers). It also creates a 120Hz tone, which it uses for the dial tone and pulses for the “busy signal” (in quotes because that is a bit off from the industry-standard).
A slightly unexpected thing that I noticed about this unit is that the conversation is not transferred particularly well between the telephone sets (after some testing, I am convinced that it isn’t just a defect in this particular unit). The only reason that I can imagine is that, in practice, the teacher would probably crank the amplifier so loud that the people using the phones couldn’t tell that they couldn’t hear each other on the actual phone (and the students would be right next to each other, anyway). In any event, if you wanted an intercom, you’re much better off just connecting a couple telephone sets in series with a 9v battery and a suitable resistor.