Old modems
are things like the Plessey (badged GPO or BT) Modem 2B (all discrete
transsitors, pot-cores in the filters, does 300 buard), or the 13A (A
300 baud modem in a plinth that fits under a Telephone 746). Actually,
those might be too modern for some people :-)
What about the old light blue metal boxes labled "Gandalf"?
Jay