Bell Intercom Conversion

[Resonator Guy]

Today I got a small Bell Sound Systems Intercom that I intend to strip and then use the parts for an amp build. It uses a 6SJ7, 6V6 and 5Y3 tube set and came with all real strong tubes. I think the tubes, including a good coke bottle 5Y3 are worth what I paid for it all. The chassis will fit into the cab I will be using and I am hoping the PT and OT are functional. Should make a neat little amp. Now here is my question. Along with a choke there is another transformer-like bit that was sealed inside a ferrous ring with a ferrous top. What is this called and what should it do? I don't plan to use it but am interested in what it is. The pictures below may help the ID.
Thanks.

[loudthud]

I could be wrong but my guess is that the mystery transformer is what in telephone speak is called a Hybrid. It allows you to speak without the signal feeding back into your speaker but your voice comes out of the remote speaker. What switches are on the front of the unit?

[Resonator Guy]

loudthud, those switches were pretty much unhooked when I got this. I believe they were for other units or speakers elsewhere, but that is just a guess. There was loose wire balled up inside that went who knows where. I just guessed it was part of an intercom and your suggestion makes sense. I just wondered what that rig was and I suppose it might work like a telephone. It won't be that way for too much longer. Winter project time is coming fast.

[loudthud]

Looking in my 1962 copy of Essential Characteristics there is a schematic in the back for an "Intercommunication Amplifier". There is a transformer on the input. In the talk mode (when the push to talk switch is pressed) the local speaker is connected to the input of the of the amplifier through the input transformer and the output goes to a remote speaker selected a four way switch. In the listen mode the remote speaker is switched to the input transfomer and the local speaker is connected to the output of the amp. So the complete system consists of the base unit and four remote units. The remote units are just a speaker and a push to takk switch. Each remote is connected by a three wire cable run back to the base unit. No way for the remote unit to get the attention of the base unit unless that unit is selected by the 4 way switch. Then you can just press the push to talk switch and the base unit will hear you.

Edit: Apon further study it seems that any remote station that activates the push to talk button will be connected to the input transformer and be able to converse with the base station once the four way switch is moved to that station.

[Resonator Guy]

Lovely! I will find out later if that input transformer can be used as output in a different application. Thanks.

[bluto]

I have a couple of similar American units that are sadly series filament and not nearly so nice as that one...anyway they have an extra transformer also and it is for the input, matches the 600 ohm standard of the Bell System IIRC so yours might be similar. That tube lineup is perfect for building a Fender 5C1 Champ clone, definitely worth the trouble.

[Resonator Guy]

And here it is, almost finished and sounding okay. no hums , buzzes or crackles.