Franks Pioneer SX-1050 Restoration

Pioneer SX-1050 Receiver 

Today were showing off the restoration of a nice Pioneer SX-1050 Receiver.  The SX-1050 released during 1976 to 1978 was the smaller version SX-1250 thats so well known and later replaced by the SX-1080 Receiver.  The SX-1050 is leagues apart the smaller 850/950 series with a much better build quality. Featuring two separate filter capacitor supplies, a large capacity , low internal resistance toroidal transformer and an unmatched RF stage!

Power Supply AWR-103 and AC/DC Stage AWR-104

The power supply is divided into the soft start feature, AWR-104 rectification stage and main AWR-103 PCB.  Like many of the assemblies on the SX-1050 there were MANY bad solder joints, baked and cold alike, this is a major detail point on the SX-1050/1080. 

AWX Surge killer assembly had a new high temp (105C) low impedance Nichicon PW 10MFD installed and new Omron relay with the original vertical chassis mount installed. The 22000/470MFD capacitors in the AC/DC stage were replaced with high temp (105) low impedance Nichicon PW capacitors with an increase in operating voltages. One of the large diameter 470MFD original caps had a heavy bloated construction. New 2A/1Kv Fairchild rectifier axial diodes were also installed.

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New computer grade Nippon Chem-Con 22,000MFD capacitors were installed as well.

The electrolytic capacitors on the AWR-103 assembly were replaced with high temp (105C) low impedance capacitors and high grade polypropylene WIMA film type with an increase in operating voltages. From a previous repair attempt noted the large TO-220 regulating devices still remained. These were replaced with heavy duty On-Semi TO-220 250V regulator devices. Modern Fairchild axial 4148 diodes were installed as well as new low noise Fairchild TO-126 and TO92/L devices installed. 

Protection AWM-090

 The SX-1050 protection employs several functions such as over current/load protection, DC deviation and short circuit applications.

All of the tantalum and electrolytic capacitors were replaced with a high grade WIMA polypropylene film and low impedance high temp (105C) Nichicon PW with an increase in operating voltages.  The relay was replaced with a low noise variant Omron MY4-48V type and associated On/Off devices replaced with new Fairchild TO-126/TO-92 low noise devices. 

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Driver AWH-047

The driver stage is mounted on a single PCB layout to the rear of the chassis. Designed as a parallel push-pull topography and a PNP differential stage and constant mirror source and a compound complimentary NPN/PNP output stage.

The electrolytic on the driver board were replaced with audio grade Nichicon KT and low impedance PW as well as decreased couplings to high grade WIMA polypropylene film capacitors with an increase in operating voltages. New precision Bourns Idle and Offset potentiometers installed as well as new constant current and new 1% matched BETA differential pair transistors with TO-92/126 Fairchild devices. Modern Fairchild axial 4148 diodes were installed.  The SVT diodes along with TO-3 mounts had new thermal compound applied and MICA insulators. 

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Flat Amp AWG-040 and Tone Control AWG-041

The input stage is a dual rail (-/+ 30V) supplied complimentary SEPP (single-ended push pull) topography with a 0dB gain populated with the volume control is a very nice enclosed stepped attenuator such as the 1250.  The Tone control 041 assembly uses a twin NFB and FET differential stage.

All of the electrolytic were replaced with audio grade KT Nichicon and low impedance PW along with high grade WIMA polypropylene films with an increased operating voltages. Larger form factor .22MFD MKP Solen high grade polypropylenes were installed to replace the original mylars. The differential stage pairs and all small signal TO-92 were replaced with Fairchild low noise TO-92 devices.

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Filter AWM-089

The filter stage, characterized with a 12dB/Oct noise reduction with a 30Hz/8Khz subsonic and high pass filter.

The electrolytic were replaced with a KT audio grade Nichicon capacitor and all original mylars replaced with a high grade WIMA polypopylene film capacitor with an increase in operating voltages. The NPN devices were replaced with low noise TO-92 Fairchild devices. 

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RIAA EQ AWF-020

The RIAA stage is mounted under the RF section with a shielded protector. It consists of a DC tired NFB circuit employing a SEPP output and differential front end. Below is a RIAA Curve Tests performed after the rebuilt of the AWF-020 PCB

RIAA CURVE RESPONSE NOTIZEN

The tantalum and electrolytic were replaced with a audio grade KT Nichicon and low impedance PW capacitors  with an increased operating voltage. All small signal devices were replaced with low noise TO-92 Fairchild devices. 

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New custom SMD LED’s to replaced the old incandescent type

AUDIO NOTIZEN