The SX-9000 was a very early released solid-state SX series from 1970-1972 and touted an impressive amount of features for a receiver of its time such as microphone dubbing (X2!), two phono stage inputs, a present tone feature for the audio front-end. The unique faceplate has a drop-drawer for the additional attenuators and control plane.
W16-028 Power Supply
The regulated power supply on the SX9K employs two full-wave rectifier stages comprised of common mode diode devices as well as a 80V full wave bridge rectified output with the initial bridge cap coupled with a 2200MFD capacitor for the B-/+ rails. The handful of 2200MFD dc coupling capacitors are actually chassis mounted in this outlay.
The initial full wave rectifiers were both replaced with a modern HexFred Ultra-Fast soft Recovery common cathode TO-220 devices with new high grade polypropylene bypass film capacitors. The failure prone TO-92 device was replaced with a more robust TO92L modern Fairchild device. All of the PCB mounted electrolytic were replaced with a low impedance, high temp (105C) Nichicon PW type with an increase in operating voltage with several coupling stage values increased for better noise suppression. Chassis mounted 2200MFD 50V< capacitors were all replaced with Nichicon PW type as well with an increase in operating voltages.
BEFORE
AFTER
Regulated Vdc Confirmation
Bridge Rectifier & Filter Capacitor
The large single B-/+ 2200MFD filter capacitor was replaced with a computer grade CDE type 2200MFD/100V capacitor. All of the original 3A diodes were replaced with modern axial Vishay 3A 1KV rectifier diodes along with new high grade polypropylene bypass film capacitors. The two parallel 100MFD/100V axial capacitors were replaced with a single 220MFD/100V radial type Nichicon PW capacitor.
BEFORE
AFTER
W28-002 Reverb
An oft-gimmick at the time for audio was the echo effect brought fourth with “Reverb” units and designs. The SX9K also uses a front display reverb indicator that would display potential crosstalk as the reverb is increased.
The failure prone 800 series NPN devices were all replaced with a modern, low noise TO92 Fairchild devices in both input/output stages. All of the electrolytic capacitors were replaced with a audio grade KT/KA Nichicon with an increase in operating voltage. All remaining films were upgraded to a high quality MKP WIMA polypropylene type film capacitors.
BEFORE
AFTER
W21-003 Mic Amp
The SX9K allows for multiple microphone inputs as well as separate input gain attenuation. With one microphone input uses the concept runs its signal monaurally through both left/right outputs.
The simplified gain stage devices were all replaced with a modern, low noise TO92 Fairchild devices. The DC coupling capacitors were replaced with a low impedance Nichicon PW type as well as audio grade KT/KA Nichicons all with an increase in operating voltages. Upgraded high quality MKP WIMA polypropylene film capacitors were installed.
BEFORE
AFTER
W21-002 RIAA Phono (HeadAmp)
The W21-002 design I have spoken of on MANY SX series as this circuit concept was used in many of the SX8XX series employing a simple NPN gain stage and RIAA EQ output.
All of the small signal devices were replaced with modern, low noise TO92 Fairchild devices. The DC coupling capacitor was increased for better filtering and replaced with a low impedance PW, remaining electrolytic were replaced with KT/KA audio grade Nichicons with an increase in operating voltages. Bypass mylar were replaced with a high grade WIMA MKP polypropylene film capacitors.
BEFORE
AFTER
W15-052 Driver Stage (PA)
Designed in the same fashion as the single symmetric PCB’s perpendicular output layouts of several other SX series. With a quasi-complimentary output and single cascade differential stage. With the parallel output design, a soft output defeat "over-protection" is employed.
All of the electrolytic capacitors here were again replaced with low impedance Nichicon PW type with an increase in operating voltages, two mylar were replaced with a high grade WIMA MKP polypropylene film capacitors. The input NPN was replaced with a low noise, modern TO92 Fairchild devices. The symmetric clipping adjustments were relocated to the foil side PCB with sealed precision Bourns potentiometers for better access during testing.
BEFORE
AFTER
BIAS Confirmation
W28-001 Tone Colour
Unique to this design is the use of preset tone filters. The SX9K has a “Flat, Soft, Bass and Vivid” 4-preset curve selector for signal attenuation that sets a specific response.
All of the electrolytic capacitors were replace with a low impedance PW and audio grade KT/KA Nichicon type with an increase in operating voltages. High grade WIMA MKP polypropylene film capacitors replaced the original mylar films. All of the small signal devices were replaced with modern, low noise TO92 Fairchild devices.
BEFORE
AFTER
W22-002 Pre-Amp (ControlAmp)
The large amount of electrolytic capacitors here were replaced with low impedance PW and KT/KA audio grade Nichicon capacitors with an increase in operating voltages. New high grade WIMA MKP polypropylene film capacitors in stalled as well. All small signal NPN devices were replaced with modern, low noise TO92 Fairchild type.
BEFORE
AFTER
RF Assemblies
Each of the chassis mounted RF assemblies had all electrolytic capacitors replaced with low impedance Nichicon PW type and high grade MKP WIMA polypropylene precision film capacitors.
AUDIO NOTIZEN
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