Hi..
I want to build stereo MPX decoder (adapter) for my Fisher FM-100 tuner. I was looking for some article in old electronics magazines but until now without any luck. If any of you old/new timers have some information where to look for that kind of magazine articles please tell me.
Thanks in advance.
Dubravko
I want to build stereo MPX decoder (adapter) for my Fisher FM-100 tuner. I was looking for some article in old electronics magazines but until now without any luck. If any of you old/new timers have some information where to look for that kind of magazine articles please tell me.
Thanks in advance.
Dubravko
There is a multiplex decoder described in RCA receiving tube manual, I have edition RC-30, it is on page 686, it use one 12AX7 and one 6CL8.
There are also the HH Scott 335, the McIntosh MA6, and the decoders from the Dynaco FM3 and the later Fishers themselves to consider. All easy builds except the ones that require precision inductors.
The circuit in RC-30 is not 100% tubed. It employs 4X 1N295 germanium diodes.
Mr. Turner provides this circuit that also uses SS diodes.
A 6AL5 might substitute for the SS diodes in either frequency doubler. A 6JU8 quad diode might substitute for the SS diodes in Turner's ring demodulator.
If 100% tubed is not essential and SS is acceptable, I strongly recommend DIYer extraordinaire S. Bench's IC based design. That setup is "idiot resistant" and a successful conclusion of the project is quite likely.
Mr. Turner provides this circuit that also uses SS diodes.
A 6AL5 might substitute for the SS diodes in either frequency doubler. A 6JU8 quad diode might substitute for the SS diodes in Turner's ring demodulator.
If 100% tubed is not essential and SS is acceptable, I strongly recommend DIYer extraordinaire S. Bench's IC based design. That setup is "idiot resistant" and a successful conclusion of the project is quite likely.
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Or Bob Fitzgerald's LM4500-based decider at FM MPX Adapter. I've built about 18 of these for various valve and SS tuners. They are great. And the price is right too.
The resonant frequency of any circuit is given at least for the Philco unit. So basically one could calculate the inductances values and proceed. But we have no clue where the tap is in L3?
Best regards!
Best regards!
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Or maybe this Fisher MPX-10 (with a Roddam detector). It only uses four RF chockes of which both the resistance and the inductance is mentioned.
Still two solid state diodes (beside the two in the power supply), so not 100% tubes.
FISHER MPX-10 Service Manual download, schematics, eeprom, repair info for electronics experts
Still two solid state diodes (beside the two in the power supply), so not 100% tubes.
FISHER MPX-10 Service Manual download, schematics, eeprom, repair info for electronics experts
Miller MX Adapter Built From Their Coil Kit
The Miller coil kit was on the market not long after the MX standard was approved. This is my build, might be around 1962. The PT & chassis are Hammond. The adapter was used with an EICO HFT 90 FM receiver till 1977 when I bought a Sansui TU717 receiver & the matching AU 717 amplifier.🙂
The Miller coil kit was on the market not long after the MX standard was approved. This is my build, might be around 1962. The PT & chassis are Hammond. The adapter was used with an EICO HFT 90 FM receiver till 1977 when I bought a Sansui TU717 receiver & the matching AU 717 amplifier.🙂
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The Fisher MPX-10 and MPX-20 work with the Crosby FM MPX stereo standard which was not selected by the FCC in the USA so they do not work with any modern FM tuner. They are basically museum pieces.
The Fisher MPX-50 and later work with the Zenith standard that was adopted and these are the ones you want to get in order to partner with a modern tuner. The MPX-100 is an external unit and can be used with any tuner. The MPX-50, MPX-200 and WX were designed to be used with Fisher tuners. The MPX-200 includes a power supply so it may be usable as an external unit with minor modifications.
You can find a write up about all this in Ron's Radios website:
https://ronsradios.com/2021/09/06/fishers-early-fm-multiplex-decoders/
Stelios
