Grundig FM stereodecoder4 hack

How to adapt a different FM stereo decoder (in this case it is a solid state decoder for Imperial 666 radio) to a Grundig Locarno FM radio (original grundig stereo decoder 4 or 5 were needed)

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Imperial 666 stereo decoder connection schematic

/forumdata/users/15003/Schermata_a_2021_02_17_13_48_18(1).png

Please note 47K resistor on the mainboard that needs to be added to the circuit above

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Grundig Locarno stereo decoder connector

/forumdata/users/15003/Schermata_a_2021_02_17_13_49_44(1).png

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grundig stereo decoder 4 schematic

/forumdata/users/15003/stereodecoder4.pdf

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Imperial 666 stereo decoder schematic

/forumdata/users/15003/imperial666_decoder(1).png

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Modern alternative with IC TA7343

you can use 6.3 Vac from pin 9 and 8 of the stereodecoder connector (Grundig Stereodecoder 4/5) with a  bridge rectifier and a big filter capacitor to obtain the CC for this circuit (pay attention to the common ground , pin 8)

/forumdata/users/15003/stereodecoderta7343axpvg.png

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Loewe stereo decoder you can also use (with 47K resistor in series to Vcc)

/forumdata/users/15003/stereodecoder52941.png

/forumdata/users/15003/Stereo_Decoder_52941_52971(1).png

Stereo-Decoder 52941 / 52971

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