Sansui 1000A Receiver Restoration

Sansui 1000A Receiver

Today were showcasing a Sansui 1000A Tube Receiver.  The 1000A came in several variations and each variation also contain about 2-3 versions of the schematic. The 1000A is not for the faint of heart to tackle and can be quite time consuming.

The 1000A features a Tube/Transistor topology, paired with a push-pull compliment of two 7591 power tubes a channel and a nice 6A/AX7 signal tubes. One of the real prized sections of the early and tube models of Sansui was the use of Hashimoto Electric output transformers and iron who still produce extremely high end amplifiers, etc.  The 1000A is regulated to a 117VAC line level so we recommend all our customer to use a voltage regulator/conditioner when operating their restored units.

One of the first issue is the 1000A utilized oil/paper and large value axial capacitors, which of the time were quite poor in construction. Also noted with 120V mains we can see upwards of 480Vdc at the plates which actually starts to exceed even the original voltage ratings. 

 All of the 7591 couple films were replaced with higher voltage, audio grade MKP polypropylene film capacitors along with the associated grid resistors which are often found to be quite out of tolerance due to the heat radiated int his stage. This is also the time we installed a 10OHM at the cathode of the 7591 to ground for a more reliable bias point which using our bias formula and the 7591 dissipation factor were looking at about 32mA each cathode or 325mV across the resistor (325/10) 32.5mA;  this is where a matched pair of tubes comes in handy.

The associated bias network capacitors were all replaced with a modern higher voltage Nichicon TVX and .33-.22 MKP audio grade Polypropylene film capacitors. A high temp (105C) low impedance radial PW Nichicon 33MFD was replaced with a higher voltage rating at the terminals versus an axial  package.

The original SW-05 diodes (X3) were replaced with an ultra-fast modern UF400# type diode and to each 220/300V capacitors which were recapped, each diode was bypassed at the caps with a .0051 PPT film capacitor.  

At this location the headphone ballast resistor is housed, on this model someone had improperly driven the 1000A causing the resistor to radiant massive amounts of heat stripping the shielding off the associated leads.  The multi-pin resistor was replaced with high grade Eagle non-inductive film resistors at 10W, we found under the ballast a AC Primary lead which had actually burnt through! What a disaster waiting to happen!

BEFORE 

AFTER

Solid State Pre-Amplifier RIAA EQ

The 1000A features a Solid State Pre-Amplifier stage with incredibly low noise BJT’s, very nice devices for quite operation, these are not point to point but PCB sections at the side of the unit.  The SM indicates preferred performance with MM cartridges and recommends the use a a input transformer for inputs of under 2mV. Each PCB was repopulated with low impedance high temp (105C) PW Nichicons and the BJT’s removed and tested for leakage, input resistors were replaced with 1% films and out of spec resistors. 

RF Front End/STAGES

The original paper/films were replaced with audio grade WIMA polypropylene film capacitors and Panasonic ECW polypropylene film capacitors at a higher 630 voltage including coupling capacitors for the controls and bypass films. 

Audio Report

Marantz 2330BD Receiver Restoration

Marantz 2330BD Receiver

Today were showcasing a Marantz 2330BD Receiver. Produced during the latter 77-79 years the 2330BD is similar to the 2330B with the addition of a multi-voltage selector for overseas markets and a Dolby FM Decoder.   These models differ from the 2330 with the integration of a single symmetric driver assembly and ,multi-section filter capacitors and of course Dolby.

P800 Power Supply

 The power supply had a new Omron MY4 installed recently which remained.  The remaining electrolytic were replaced with higher voltage high temp (105C) long life/low impedance Panasonic FC and PW Nichicon to better withstand the offset temperatures within the power supply. Diodes upgraded to modern 4148 or ultra-fast 400# series. The original common-cathode/anode devices were replaced with higher capacity, more robust MUR1620 series TO-220 devices.  The 2330BD uses a dual section fitter capacitor array for each rail/channel, these were restored with 7200/100V computer grade CDM Cornell capacitors. The bridge rectifiers were updated with high grade MKP polypropylene film capacitors at .1MFD

P700 Driver Assembly

The driver assembly comprised on a complimentary PP output section is mounted to a single sink with a symmetric topology.

The initial differential pair transistors were replaced with new lose noise TO-92 1845 transistors thermally coupled and matched to 1% along with the regulating transistors to the above.  The pre-drivers were also replaced with modern more robust MJE devices and new thermal compound to their respective heatsinks.  2473 type diodes were replaced with modern 4148 diodes and the robust original potentiometer cleaned and lubricated and tracking confirmed. High grade WIMA and Panasonic ECW were installed in place of the original films and electrolytic replaced with low impedance high temp (105C) Nichicon PW’s.  TO-3’s removed and new thermal compound.

P400 EQ RIAA

Like many of the latter designs the selector is housed on the same assembly as the EQ stage.  1% matched modern low noise 992 high gain transistors were replaced for the initial gain stage.  The remaining electrolytic were replaced with low impedance long life and audio grade PW/KA capacitors. Below is the only RIAA curve report published online to date we compiled;

RIAA Curve Report

PE01 Tone/Pre & PH01 Filter/Switching

The differential gain stage is comprised of a single package dual device and output, similar PCB design to latter 23XX series except the amount of onboard attenuators housed making for a large footprint PCB.  The electrolytic and tantalums were replaced at 1MFD with high grade WIMA polypropylene films and Nichicon KA audio grade capacitors and two .22 polypropylene ECW film capacitors.

The Filtering and Switching Assembly access is gained after removing the PE01 assembly and the time we cleaned and lubricated each control and switch using Caig Labs D5/F5 concentrates. The electrolytics were replaced with low impedance PW's and high grade polypropylene WIMA Film capacitors. 

RF Sectionals

The RF stage is a separate FM Front end PCB and AM/FM Decoder DBX assembly similar to the 2385+ series more so.  The several bi-polar electrolytic were replaced with .22MFD ECQ stacked films and UPV BP Nichicon. Remaining electrolytic with high temp (105C) KL/PW Nichicon capacitors.

Pre Restoration Performance Report

 Restored Performance Report

Two Pioneer SX-1250 Receiver Restorations

Two Pioneer SX-1250 Receiver's

Here we have two Pioneer SX-1250 Receivers. One unit came in with blowing fuses and required a little extra attention. This particular unit received new OnSemi TO-3 output devices and 3rd order drivers, as such we were able to obtain a final harmonics distortion and a slight increase in performance with original biasing. 

Stabilizer AWR-106 and Power Supply AWR-107

The SX-1250 features a potted toroidal power transformer with no discernible slew inductance and isolations tied to separated bridge rectifiers. Also integrated is a reserve of 44,000 microfarads per side!  The original capacitors all reflected signs of venting at the terminal junctions.  

The filter caps provide some of the most critical paths in the receiver to provide filter smoothing and power reserve for the push-pull operation at all frequencies.  For comparison we may see 25Vrms at kHz but at 20Khz that may extend to -/+ at 30Vrms or drop at sub sonic frequencies so these couplings are paramount for optimal operation. 

Also noted, one of the units had a small 22K/80V filter capacitor installed from a prior repair somewhere, unfortunately they cut the original bracket down so some improvising was due.  The new 22,000/100V Nippon filter capacitors were installed in each unit, a new 50-60mm clamp was secured and tapped under the original clamp for a clean flush look.

InRush Current Notation**

 The SX-1250 also employs a 48V LS soft start relay to limit the large inrush current attributed from the low inductance to high 22K filter caps, this charge period can generate several hundred amperes, a large limiting 30W resistor thermal coupled to a thermal fuse triggers the array. The housing was removed which is a chassis mount and points brandished.

AWR-107 Power Supply

The power supply is initially comprised of two 470MFD axial capacitors. These were replaced in the units with new Vishay high temp (105C) axial capacitors, we choose a higher temp, higher voltage opponent for a more robust application as well as a smaller package due to the large current limiting 3.3OHM 30W resistor on the same assembly.  Due to this large limiting resistor all of the foil side points should be reflowed as we did and cleaned. The remaining 470MFD caps were replaced with new high temp (105C) long life PW Nichicons capacitors.  

AWR-106 Stabilizer

The monolithic output stabilizer PCB is the +65V rail supply.  We replaced the TO-220 regulating 2SB/2SD devices to modern , heavier duty and OnSemi 15X32/33 devices for long term reliability with new MICA squares and thermal compound. New modern Fairchild TO-126 1220/2690 npn/pnp devices were installed and the 2473 diodes replaced with general 148 type.  A 1000MFD axials were replaced with TVX Nichicons and remaining radials electrolytic to high temp (105C) long life PW capacitors.

Protection AWM-091(A)

The protection circuit of the SX-1250 employs a muting function for speaker protection during power up. The protection also extend to impedance or load shorting and primary output failure and point detection overload.

Each protections relay was removed and replaced with a new low noise variant  MY4 Dpdt Omron relay for smoother, quite energizing. The TO-126 devices were upgraded with more reliable modern 2690 devices and a 2383 TO-92L small signal replacement. The electrolytics were replaced with high temp (105C) long life PW Nichicons and remaining 2473 diodes replaced with general 4148 type.  On of the assemblies had obvious repairs performed with incorrect resistors which were replaced with metal film Vishay type and all solder points reflowed.

Power Amp Assemblies AWH-048

The SX-1250 employs a reliable driver section and after rebuilt hundreds factor of distortion which is impressive at over 150W on any unit.

The driver uses a tied pair of pnp differential inputs which were replaced with modern low noise Fairchild TO-92 992’s matched to 1%  and a constant current grouping. The bias feedback network has a problematic 2SC869 TO-92 device which as replaced with a modern Fairchild low noise 1845 device, on unit had this replaced with metal cylinder TO-18 device which is a poor cross reference! the pre-driver compliment was replaced with TO-126 3503/1381 devices. The 2473 was updated to a modern 4148 diode as well. The darlington array driver pairs 2sb/630 and 2d610 were leaky and mismatched in one of the two units, these were replaced with both channels per DUT with heavy duty, OnSemi 15X32/33 TO-220 devices. the PCB with notated repairs also had several wrong type resistors which were replaced with 1W to 1/4 metal film and MOX type resistors. 

Remaining films were replaced with high grade MKP polypropylene film capacitors (.1/1MFD) and the tantalum to a high temp (105C) KL nichicon electrolytic.  Remaining electrolytic capacitors were replaced with high temp (105C) long life PW Nichicons. Both 470OHM pots were replaced with modern precision Bourns trimmers as well.  Again the PCB with noted repairs had an incorrect pot installed which was updated.

TO-3 Output Devices

The problematic channel DUT was noted to have one bank of original NEC outputs while the working channel had a mismatch of toshiba and RCA TO-3 devices. Half of the NPN/PNP NEC compliment were shorted.  The entire unit was updated with heavy duty high performance OnSemi MJE15X24/23 devices and new mica/thermal compound applied.  The upgrade in driver and output devices put this unit just a step ahead in final performance (please reference below verification reports)

RIAA EQ AWF-021(A)

 As we’ve discussed on this unit before the SX-1250 RIAA EQ stage is well designed. using matched pnp differentials, polystyrene and metal film resistors in a SEPP topology for a THD at .1% rated output. 

The initial differential gain stage were upgraded to modern low noise Fairchild T)-92 992 devices match to 1% hfe grouping.  Different input polypropylenes were used in these rebuilds to a high grade Panasonic ECW polypropylene film capacitors. Remaining electrolytic capacitors were replaced with low impedance long life PW’s and audio grade KA Nichicons. Remaining 2473 diodes were replaced with modern 4148 diodes. 

Flat Amp AWG-042 & Control Amp AWG-041 

The initial stage flat amp consists of multi-tiered , tied differential input and 2-stage JFET (2SK30/34 used) The control features a sub-sonic through ultra-high frequency attenuation called Pioneers twin-tone system.  A high grade enclosed 32 stepped, decibel logarithmic volume potentiometer is installed. 

 The electrolytics at 100/220/470MFD filter stage were replaced with a long life high temp (105C) Panasonic FC’s.  The small signal AF with low impedance long life PW and audio grade KA capacitors. KL 2.2/MFD values were utilized on the Control amp assembly.  Panasonic ECW 1MFD high grade polypropylene film capacitors were upgraded on the AWG-042 PCB.  2473 diodes were replaced with modern 4148 general diodes.  Both stage differentials were updated to modern Fairchild 1845/992 TO-92 devices matched to 1%.

Filter AWM-089 & Function PCB AWS-094

With the above assemblies splayed on the chassis you can access both push-switch assemblies. As with the above AWG-042/041 assemblies the rotary and push switches were all deeply cleaned and lubricated using Caig Labs 99% D5/F5 and 99.9% anhydrous alcohol. 

The few electrolytic (220MFD on AWS-094) and the filter amp were replaced with audio grade Nichicon KA and low impedance PW capacitors.  Both TO-92L 1313 devices were replaced with modern low noise Fairchild 1845 devices.

RF Stage AWE-689

The RF stage in the SX1250 is better than any SX series to its range, with a multi facet gang fm/am tuning capacitor and dual MOSFET HA IC’s gain stages and multi tiered phased ceramic filters.

A large number tantalum capacitors (.1-.68) were replaced with high temp long life KL Nichicons and remaining values with low impedance PW Nichicon’s. The tuning gang was slowly cleaned and debris’ed. 

New LED’s were installed in heavy use indicators and front dial display

Audio Notizen