Modem 13A

I also came across that Modem 13A that I mentioned a few days ago, the one that's a plinth under a normal 746 telephone. The phone part is pretty normal, apart from having 2 buttons on top, in front of the handset rest, labelled 'TELE' and 'DATA'. They are interlocked so that presing one releases the other, and both are released buy the heandset rest. The 'TELE' button operates a microswitch, the connections of which go nowhere, the 'DATA' buttom operates a multi-pole changeover switch, again most of the contacts aren't used. The rest of the phone is what I'd expect in a rotary-dial 746. The base of the plinth comes off by 4 captive screws. Inside is a PCB, component side down (so you can see the components when the base is removed), also hald in by a further 4 captive screws. There are 8 wires seems to indicate that 2 of them are used to externally power the modem (it can be line-powered) -- these wires go to 2 otherwise unused terminals on a terminal strip, 4 of the wires are to be linked in 2 pairs (again done on said terminal strip) and the remaining 2 wires go to the line (presumably via that DATA switch. There are 4 terminals on the PCB that go to a cable that comes out the back. The label gives the 'CCITT circuit numbers' for each terminal, I've not looked them up yet, but they're going to be normal RS232 signals. The PCB contians a number of discrete transistors, a number of 8-lead TO99 cansm which I susepct (from the part number and connections) to be 748 op-amps and a single 14 pin DIL device, which might be something like a 7403 (???) And a lot of pot-core inductors and strange-value poiystyrene capacitors, presumably for filtering. -tony