Charlie:
I don't think that Valcom bought the rights to these things, I think that Melco just discontinued the R, T and RT units when Augat bought them in the early 1980's.
Remember that Tone Commander, Teltone and Melco were huge suppliers of these things to Bell companies and independent telcos, while Valcom catered more to interconnects. I think the fact that telcos dropped these things like a hot potato (after divestiture) made Valcom appear to have been the sole survivor.
For the most part, Valcom and ITT were in fact the only companies who continued making 1A2 intercom equipment after at the time. I think it's safe to say that Valcom is the only remaining manufacturer of these things but it's been over five years since I have purchased one so I can't say for sure.....
