Paul's Sansui 5050 Receiver

Sansui 5050 Receiver

Today were showcasing a customers Sansui 5050 Receiver that came in for a restoration. The 5050 was released from 1976 to 1977 with a modest output rating of 33W @ 0.5%, the 5050 is favored among many Sansui owners for its incredibly warm and lushes sound.

F-2700 & F-2701 Rectification/Protection and Power Supply

The 5050 was released in a few batches utilizing a different power supply topology. This model used the separate PCB designed F-2700 and F-2701 design while the majority use the F-2649 assembly.

The F-2700 PCB is populated with the dual full wave rectification supplies tied to the 6800MFD filtering capacitors and F-2701 PS, mounted perpendicular to the F-2701 via pin headers. I like this separation of noise prone rectification from the main PS, its a solid design.  All of the diodes including the 1A and 3A axial were replaced with Vishay Ultra-Fast, Soft Recovery type for a decreased noise floor, with the decoupling increased to a 100MFD from 47MFD and all electrolytic replaced with a high temp (105C) low impedance Nichicon PW and Bipolar VP with an increase in operating voltages. The MV-13 epoxy diodes were replaced with general axial Vishay 4148 diodes. The remaining TO-92/L devices were replaced with a modern, low noise Fairchild TO-92 and TO-126 for better dissipation.

BEFORE

AFTER

On the F2701 PS, like MANY Sansui’s all the fusible resistors in this supply were removed and replace with 1/2Watt KOA carbon film resistors including the 6.8 and 2.2 (parallel values.)  All of the electrolytic capacitors were replaced with a high temp (105), low impedance Nichicon PW capacitors with an increase in operating voltages. The relay was replaced with a high quality Omron MY4 type.

BEFORE

AFTER

F-2647 Amplifiers

The 5050 mounts the driver assembly, again perpendicular with pin headers to the F-2701 assembly with a separated TO-3 mounted heatsink for the output stage. The amplifier stage is made of a common-emitter PP stage.

The initial differential pair transistors were replaced with matched Fairchild TO-92 devices at 1% and beta mapped, constant current devices were replaced with a ultra-fast ZTK type TO-92 and remaining drivers with a modern low noise Fairchild TO-126 devices.

Beta Mapping

 The adjustment pots were replaced with precision Bourns potentiometers. The fusible resistors again replaced with KOA 1/2W carbon film type. All of the capacitors were replaced with a audio grade Nichicon KT and VP Bipolar type with an increase in operating voltages. The input coupling capacitors were replaced with a high grade WIMA polypropylene film type. 

BEFORE

AFTER

BIAS Confirmation

F-2646 Tone-Amp

The tone amp features a three-way tone control and high-pass filter with  loudness tapped volume pot. The pre-amp is a simple NPN tiered gain stage output.

All of the small signal devices were replaced with a low noise, modern TO-92 Fairchild devices. The .047/.47 coupling.bypass mylar were all replaced with a high grade WIMA polypropylene film capacitors. All of the electrolytic were replaced with a audio grade KT and Fine-Gold Nichicon as well as the decoupling filter cap to a Nichicon PW which was increased to a 330MFD for a better noise floor, all with an increase in operating voltages. 

BEFORE

AFTER

F-2644 RIAA EQ & MIC Amp

The phono stage and Mic Amp circuits share a PCB assembly mounted under the chassis to the sub-chassis side wall oddly enough, far enough away from the PS but very very close to the RF stages…Similar built using a tiered NPN gain stage.

All of the electrolytic capacitors in both stage were replaced with audio grade Nichicon KT and Bipolar BP, the decoupling was replaced with a low impedance PW and increased to 330MFD for a better noise floor, all with an increase in operating voltages.  The output coupling stage capacitors were replaced with a high grade WIMA polypropylene film capacitor. All the small signal devices were replaced with a low noise, modern TO-92 Fairchild devices. 

BEFORE

AFTER

RF Stages

The 5050 has a simple but very solid super-heterodyne RF stage with a complex sensitive IC front end. All of the electrolytic in this stage were replaced with a high temp KZ and low impedance high temp (105C) PW Nichicon capacitors with an increase in operating voltages.

New custom SMD/LED’s installed to save the original plastic house from melting in the future, as is common with Sansui the Fuse lamp mounts had to be reflowed as the original incandescent bake the solder joints.

AUDIO NOTIZEN