After reading the thread about Stephen J's 100-T which, at some point, turned into a thread on Fisher's MPX adapters, I thought now might be a good time to start a dedicated Fisher MPX thread. Fisher's first MPX adapter, the MPX-10 came out in 1959 (perhaps as a 1960 model). It was designed to work with the Crosby multiplex system; then used by a handful of broadcasters who were experimenting with it at that time. It is the model Fisher recommended for use with both the 1960 Custom Electra III and the 1960 Premiere in their owner's manuals. It is a 5-tube model comprising 4-12AX7s and 1-12AU7. The MPX-20 came out in 1960 specifically for concealed installations. Also intended for the Crosby system reception, it was designed to fit right into the chassis of the FM-100, 100-T and 202-T. It's curious that the 101-R tuner isn't mentioned. It is a 4-tube model using 12AX7s. The MPX-100 was being advertised as early as May 1961 (only a month after the FCC decision) alongside such models as the TA-800, 500-S, FM-200 and the FM-50. It is a "Universal" MPX unit designed to work with any high quality, high fidelity FM receiver or tuner. The 1962 President used it conjunction with a 202-R tuner. I know I have seen an image of that control panel somewhere but I can't seem to find it. It is very impressive. The MPX-100 is a 5-tube unit consisting of 1-12AT7, 1-6AB4, 1-6AU6, 1-ECH84 and 1-12AX7. The MPX-200 was a 4-tube version of the MPX-100 designed for concealed installations. Despite having one less tube, it has the same specs as the 100. I don't have a firm date for its release but it was out in time for the 1962 model year. Fisher put out a pamphlet on FM Stereo Multiplex for the 1962 model year (copyright 1961) which goes into some detail on the subject. The following are some pertinent sections: In 1963 there were three different, new MPX units: MPX-60, MPX-65 and MPX-77. All were 3-tube units with the MPX-60 consisting of 2-12AT7s and 1-12AX7. Both the MPX-65 and -77 use 3-12AX7s. I only know of MPX-60 units from the high-end consoles like the President VIII, Regent and Executive VIII - though perhaps they were also used on the very high-end tuners like the R-200 (Perhaps you could check when you get a chance, Jon). The MPX-65 is quite common, occurring in the ubiquitous 400, 500-C and 800-C receivers as well as in all of the mid-line 1963 console tuners. The MPX-77 was used in the low-end console units like the Diplomat and the Philharmonic III. The MPX-65 and MPX-77 carried over into 1964. I'm not sure about the MPX-60. Further research is required. In 1965 the new 2-tube MPX-125 was being used in the mid-line consoles. The MPX-77 continued on the low-end models. I'm not sure if there was a premium MPX used in on the high-end consoles. Again, further research required. And I realize now that I didn't look at 1966 but I suspect that solid state MPX units would have made their appearance by this time. I doubt whether they had individual model numbers and were most likely an integrated part of the chassis. The MPX-77 or MPX-125 may have survived on the still-tube Philharmonic and the MPX-65 was certainly still available on the 400, 500-C and 800-C at this time. Did Fisher ever produce a separate, solid-state MPX unit? I rather doubt it. Further information, corrections, clarifications or questions welcome.