Quad Multiplex Decoder (MPX) For Use With A Quad FM1 Or Quad FM2 Tuner

This is a Vintage, 1960s, Quad Multiplex Decoder (MPX) For Use With A Quad FM1 Or Quad FM2 Tuner,  in conjunction with a Quad 22 Control Unit, made in Huntingdon, UK, by the Acoustical Manufacturing Co.Ltd (QUAD)- sold for spares/ repairs.

It is a solid-state add-on unit which converts the mono valve Quad FM (FM1/ FM2) tuner for stereo FM multiplex (Zenith-GE pilot tone system) reception when used alongside the Quad 22 control unit.

Approximate Size (WHD):- 8.5 x 5.2 x 18cm

It is sold without a box nor instructions, and is untested. It would probably require new internal componentry due to its age and lack of use. The inside is also pretty dirty / dusty and needs a good clean. This has been in my hubby's collection but I've no idea where he stored it as my housekeeping skills are not that lacking as to create this level of dust! The price has been adjusted as a consequence.

This could be a nice restoration project for the vintage HiFi enthusiasts: see Keith Snook's excellent article on restoration / upgrading- https://keith-snook.info/quad-fm1-stereo-mpx-decoder.html. 

Its internal mono-stereo electronic switching operates remotely from the QUAD 22 controls, so it may be placed within the equipment cabinet without need for access post- installation, or it can be attached directly to the rear cover/chassis of the FM tuner-(see appended schematic).

Summary Specification For the Multiplex Decoder

• Serial No. 4579
• Transistors: 3
• De-emphasis: 50μS (European standards) 
  
• Output voltage: 100mV (Nominal for 30% modulation) into 100K ohms
• Crosstalk: Better than 30 dB at 1 kc/s
• Suppression: 19 kc/s
• Pilot tone better than 36 dB 38 kc/s 
• Switching tone better than 40 dB
• Power requirement: 330V DC, 8mA mono (from Yellow channel HT) plus 9mA stereo (from Blue channel HT

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