Omrom programmable terminal -joke

I don;t see why that's particularly difficult (or indeed novel). One of my old modems (A 'Modem 2B' for those who care) uses discrete transistors, LC filters, and relays for the control circuitry. It usses the normal CCITT 300 baud tones, and will work with many more modern modems. It would be pretty easy to make that sort of thing using valves. Radio amateurs (at least over here) used valved FSK modulators and demodulators for RTTY work (Radio TeleTYpe). Although they didn't use the normal tones you'd use on the phone systemm, I claim those are modems. I am pretty sure some old RSGB Radio Communication Handbooks (and maybe the RSGB Teleprinter Handbook) contain schematics. Maybe similar ARRL books do too, I don't have them. I see no reason why it has to use solid-state diodes. -tony