Today were showing off a recent customers Sansui G-22000 Receiver Restoration. The G-22000 and G-33000 receivers were two of the biggest receivers manufactured during the height of the most receivers wars, released from 1979 to 1980…Considered often with the likes of the SX-1980, 2500 and 2600’s by Pioneer and Marantz.
According to Sansui, their approach to the design intentions of the G-22/33K receiver was musical reproduction. Their design concept revolved around what Sansui called the best “test instrument ever invented-the human ear.”
The G-22/33000 receivers have a unique construction, by separating the actual driver/power supply and front end AF/RF stages. The rear of the unit houses an active fan in an attractive Noir-Decco aesthetic, also containing two separate wound toroidal transformer and the separate AC/DC power supplies. The front end houses the entire AF and RF circuits. Each unit can be operated separately but not independent as the rear driver section has a 30V starter via the umbilical connector for the soft start/power circuit.
F-2819 AF PS
The G-22000 features three separate power supplies, one for the front end AF (Audio-Freq.) assembly and two independent power supplies for each driver channel! The front end Power supply is connected to the rear assembly via an umbilical connector that supplies an initial 30V source to the soft start relays sending power to the toroidals.
One of the biggest upgrades to a power supply is updated the old worn out TO-220 power regulators. Each of the original 2SB/SD devices were replaced with robust, heavy duty On-Semi MJE TO-220 NPN/PNP devices with new thermal compound applied. Original 10D1/2 diodes were replaced with UF (Ultra-Fast) Fairchild axial diodes 400X series. All of the small signal devices were replaced including the somewhat fault prone 2SC945 to a better TO-92L Fairchild device for better dissipation. All 2071/939 devices were replaced with power supply/heavy voltage oriented MJE3XX series TO-126 Fairchild device. The original relay was replaced with a low noise Omron MY4 type.
All of the electrolytic were replaced including the large 2200MFD to low impedance, high temp (105C) Nichicon PW capacitors with an increase in operating voltages and high grade WIMA polypropylene film capacitors.
F-2093 & F-2092 DRIVER PS / PROTECTION
The separate driver power supplies are derived from two separate isolated toroidal power transformers and two independent power supply, rectification stages. These assembly also house the driver protection stages and initiated vie the front end 30V trigger to the soft start relays. The G-22000 / 33K features a quad protection circuit; Overcurrent Detection, Output Short detection, thermal run away and a DC Deviation detector.
Confirmation of the 81Volt +/- supply source after rebuild
Each assembly contain 2 Omron LY relays which were all replaced with low noise Omron MY2-24V relays. Similar to above each assembly houses two and three 2SD/2SB TO-220 regulator which were all replaced with a heavy duty, robust On-Semi MJE TO-220 regulators with new thermal compound applied. Remaining 945 type devices were replaced with a new better handling TO-92L Fairchild NPN devices. All remaining 939 and 2071 devices were replaced with new heavy voltage oriented TO-126 MJE3XX Fairchild devices. Original 10D1/2 diodes were replaced with UF (Ultra-Fast) Fairchild axial diodes 400X series.
New TO-220 regulators installed
All the capacitors were replaced with Nichicon VP Bipolar and low impedance Nichicon PW capacitors with an increase in operating voltages. New high grade WIMA polypropylene films were also installed as well as removing the 4.7OHM fusible resistors and installing 1/2W KOA carbon films. In addition the R27 330OHm resistor was replaced with CF 1/2W KOA, this location is often stressed and fails.
SOFT START FAILURE NOTATION
When excessive current occurs from either failed output, etc the soft start circuit will short the inline 3.9OHM 25Watt fuse. Expect to find a shorted 3.9 if you have a failed output stage
The original rectification stage uses two 15,000MFD capacitors a side with a 1MFD bypass capacitor installed (+10KPARA OHM.) New computer grade Nippon Chem-Con 22,000/100V filter capacitors were installed with high grade MKP polypropylene film bypass capacitors installed.
F-2892 PEAK METER
Touted as featuring “professional grade” Meters, the G-22K has a reliable Peak to Peak (Pvv(rms)) meters from .1-600W/rms. The control is a Sony CX-067 IC (also used in the TOTL TA-E7!)
New precision Bourns 47K pots were installed along with all new low impedance high temp (105C) Nichicon PW capacitors with an increase in operating voltages. At this time each meter was removed, cleaned and the gimbal checked for proper deflection action.
New custom SMD type LED’s were installed for the dial/meter displays.
F-2900 & F-2901 DRIVERS
One of th biggest highlights of the driver design is the integration of Sansui’s proprietary Diamond Differential DC Circuit. The drivers use a dual JFET 2SK129A as a differential gain stage to the diamond differential (proprietary design) to a push-pull driver compliment. The output is in a OCL- darlington configuration.
As with the PS stages, the 939/2071 devices were replaced with new heavy voltage oriented TO-126 Fairchild NPN/PNP devices. All remaining 872/1175 devices were replaced with modern, low noise Fairchild TO-92 NPN/PNP devices and remaining drivers replaced with a heavy duty, robust TO-220 On-Semi MJE series devices with new thermal compound applied.
Confirmation of the 15mV(-/+5) idle bias current
New precision Bourns trimmers installed for bias/offset along with new 4148 axial modern diode replacements. Mylar films were updated to high grade WIMA polypropylene film capacitors with an increase in the coupling stage to .1MFD/250V high grade polypropylene film capacitors.
3rd order driver cross reference comparison with new On-Semi TO-220 devices
(increase Beta (hFE) range with linear current/voltage ranges achieved)
PNP MJE15033 & 2SA968
NPN MJE15032 & 2SC2238
Remaining electrolytic were replaced with audio grade Nichicon Fine Gold and low impedance, high temp (105) PW capacitors with an increase in operating voltages, 1MFD> were all replaced with high grade WIMA polypropylene film capacitors.
New TO-3 Modern, High Quality On-Semi MJE class output devices installed on failed right channel after a output tests failure.
F-2890 TONE CONTROL AMP
The tone controls after a three way nominal Bass/Mid and treble attenuation with a featured Flat bypass tone switch for a linear response. The Tone control assembly uses a ribbon feed to connect the actual tone potentiometers which were cleaned and lubricated along with all other switches using Caig Labs D5/F5 products.
Different than above due to application the 2071 devices were all replaced with a audio centered, low distortion TO-126 Fairchild NPN devices along with the 872 devices to modern low noise Fairchild TO-92 PNP devices. All of the electrolytic were replaced with a audio grade Nichicon KT and VP Bipolar with an increase in operating voltages. All the original mylar were replaced with a high grade WIMA polypropylene film capacitor.
F-2899 FLAT AMP & F-2888 FLAT AMP MOTHERBOARD
Similar to the RIAA EQ, the Flat AMP response/current stage has a left and right separate assemblies for decreased noise and a main Motherboard point. The F-2899 Flat amp assembly uses a 2SK129A JFET differential gain stage in a push-pull output configuration for a totally linear response output.
The 220OHm pots were replaced with precision Bourns trimmers as well at all small signal 872/1175 devices to modern, low noise TO-92 Fairchild devices. The driver 939/2071 devices were all replaced with audio centered, low distortion MJE3XX NPN/PNP TO-126 devices.
The original mylar were all replaced with high grade MKP .22MFD polypropylene film capacitors along with high grade polypropylene WIMA film capacitors. Electrolytic’s were replaced with Fine Gold audio grade Nichicon 100MFD capacitors with an increase in operating voltages.
The F-2888 motherboard had both 470MFD capacitors and coupling .1MFD mylar films replaced with a high grade MKP polypropylene film capacitors and new low impedance Nichicon PW with an increase in operating voltages.
F-2880 RIAA EQ (PHONO) & F-2884 RIAA EQ MOTHERBOARD
Extensive design went into the RIAA EQ stage, employing 13+ devices including a differential 2SK131 dual JFET. All configured with a constant current source and bootstrapped (piggybacked.) The RIAA EQ has a reported response at 87dB S/N Ratio with +.2dB/-0 20Hz-20kHz
The large esoteric 4.7MFD film was replaced with a high grade 4.7MFD MKP polypropylene film capacitor which requires proper dressing and fitment to avoid any noise pickup or intrinsic potentials, remaining mylars were replaced with a high grade WIMA polypropylene film capacitor. The electrolytic were all replaced with a audio grade Nichicon KT audio grade capacitor with an increase in operating voltages.
As done above, the F-2884 motherboard had both 470MFD capacitors and coupling .1MFD and .047 mylar films replaced with a high grade MKP polypropylene film capacitors and new low impedance Nichicon PW with an increase in operating voltages.
AF Stage JFETS 2SK129A & 2SK131
Below we removed and took a closer look at the dual assembled TO-92 type dual 2SK Jfets.
As we can see from the current boding the initial match of the pairs was spot on and consistent with no premature noise or break down another in either X4 devices in the AF stage. The drivers also each use a 2Sk129A JFET as a differential driver stage.
F-2886 VOLUME / 2NDMIC AMP & F-2885 MIC/1STamp
The volume attenuator employed in the G-22000 and G33K is of superb design, a potted, 32-stepped precision 4-gang potentiometer housed on the MicAmp circuit.
The volume pot was desolder to proper cleaning with the protective shield removed and lubricated with Caig Labs products.
The Micamp circuit had the original 872/1775 devices replaced with modern low noise Fairchild TO-92 NPN/PNP devices. The electrolytic were replaced with a audio grade Fine Gold and KT Nichicons and low impedance PW Nichicon with an increase in operating voltages and high grade WIMA polypropylene film capacitors.
The F-2885 Mic amp stage had the attenuator cleaned and lubricated. The original 872 device was replaced with a modern, low noise Fairchild TO-92 PNP and electrolytic to a audio grade Nichicon KT with an increase in operating voltages along with a high grade WIMA polypropylene film.
NOTE SANSUI SPECIFICATIONS DO NOT ACCOUNT FOR "RECEIVER" SPECS BUT ONLY AS SEPARATE ASSEMBLIES. NOTATE I PERFORMED A "RECEIVER" FREQUNECY RESPONSE CURVE BELOW)