If I bought an old TI 99/4a monitor, would it use the RF modulator and cable, or was some other cable type used?
The TI Monitor does not use the RF Modulator, it is a separate and different cable. The TI Monitor Cable has the same large round 5pin connector as the modulator but ends in two RCA style plugs (like the ones on a stereo). One RCA plug is for video and the other one is for audio. Please note that the TI Monitor does not have an RCA plug for audio, it has a headphone jack. You will need to go to Radio Shack or other electronics shop and buy an RCA-to-Headphone adapter which is pretty cheap. If you need a cable you can buy one directly from Allan Kresock who makes them for about $5.00.