Two questions for you guys:
1. If the 82 connecting block was designed to make the 4A a "plug 'n' play" device, what was the Model 80 control unit designed to do?

2. As a corollary to the above, if you have a 680 transmitter that has had the amp plug cut off, is there any way to hard wire it to an 82 connecting block? I notice that there are a lot of screw terminal there besides the two a.c. terminals for the 85 transformer input. Could any of these be used for the 680? Also I have a 683 that has all spade tip connections. Would the Model 80 be used for this or the 82?

Do you have a photo of the Model 80 control unit? I am not familiar with that one.

Outwardly it looks like the Model 55 control unit. Go to the TCI library and look under 4A speakerphone. They have the BSP on the 4A with a photo, etc. My problem is I'm not savvy enough to know what all the terms mean that they're using.

OK, here goes:

Since I can't guess which terms you don't understand, (you could tell us) I'll take a stab that you do not understand what a 4-wire set is. The 80-type control unit is described as being an adapter that allows the 4A speakerphone, generally used in conjunction with a 2-wire set, to be used with a 4-wire set.

A two-wire line is what we all know as a POTS line. It has a Tip and a Ring, and it uses the hybrid coil in the phone's network to derive the transmit and receive functions, and to provide just the right amount of sidetone to the user.

A 4-wire set is attached to a a 4-wire circuit, with a separate transmit pair and a receive pair, for the purposes of being able to control the gain on the transmit and receive functions separately. 4-wire circuits are generally used for private-line service and secure government lines. Sometimes the tel set is equipped with a push-to-talk handset, and a relay inside the set that switches the talk and receive functions, in a half-duplex method. The 568HAA (rotary dial), 2568HAA (12-button dial) and the 3568HAA (Autovon dial)were such sets.

What the BSP is telling us is that the company recognized that there might be a market for the 4A speakerphone set-up on not only 2-wire circuits, but also on 4-wire ones. The 80-type CU makes an electrical adaptation within itself to allow a 4-wire tel set to be compatible with the 4A circuitry which is inherently for 2-wire applications.

What is potentially confusing to someone who does not speak fluent Bell Telephonese, is the use of the term "control unit" to describe the 80-type. Since it looks like a 55-type, and since it's CALLED a control unit, one might naturally assume that they have similar functions. It is not a speakerphone control unit in the same sense that a 55 is. It does not perform the same function(s).

The 4A speakerphone, by design, eliminates the bulky 55 type by having all the electronics in the speaker part. The 80-type is, as explained above, a device that creates a 4-wire set-up from a 2-wire circuit. It should have been called an "adapter" rather than a control unit.

Just another case of needing a time-machine to go back and set the boys at the Labs straight. Too late, I'm afraid.

Good catch Arthur! Besides Government service, 4 Wire lines were also used extensively by the radio & tv networks for overseas communications with correspondents where they wanted better quality circuits (usually live broadcasts).

Sam

Thank you for explaining that to me. So basically a 80 control unit really is no benefit to me unless I have a 568 phone or equivalent, right? I thought perhaps it was used to wire up non-amp plugs.

Hi again,

Was the Western Electric 149B adapter (I think that it is a breakout device to install on a 25 pair cable run) used for the speaker phone system (4A)?

Thanks,

Joe

Joe -

I really can't remember exactly what the 149 Adapter was originally designed for. I believe it was designed for the 3B Speakerphone (it predated the 4A by years). It's use made the Violet pairs of the cable accessible on screw terminals.

Ed or Arthur will know for sure.

We mostly used it when we had a key set on a 25 pair cable going to a location and we needed to "pull a pair" (or 5) out neatly. Using it meant you didn't have to butcher the cable or go into the screw terminals on a set.

If you had a 25 pair cable with NO set attached and needed a pair or three (a single line set or two), you could use a 153 adapter.

Sam

Sam, you is correct on all points.