New: In Kit form Designed to replace the STK-0050-II in the Pioneer SX-780 and other stereo receivers using the old Sanyo module They have been successfully used in Fisher, Technics amp and receivers Eliminates the probability of poor quality modules Discrete design allows for easy repair, improves reliability and performance Can be used with many amplifier front-ends to make a complete amp. This design can be used as a substitute for the original STK-0050.  The difference is that the (II) version is a 3-emitter follower (3EF) design compared to a 2EF.  The benefits of the 3EF design are that it has lower distortion since the voltage amplifier is not loaded down as much as in a 2EF design.  It’s better for higher current and lower impedance loads.  You need special tools such as a soldering iron, DC voltmeter, side cutters, needle nose pliers, screw drivers etc. Prior Audio Electronic knowledge and interpretation is helpful. There is help at Audiokarma Will ship these complete kits International Note:  All Electronic Components are supplied Listing is for two blank PCB's, heatsinks, all parts, wire, documents, assembly instructions for two modules Free support and no returns. The module will improve the amplifier's reliability and operational specifications for stereo's using STK modules, up to 75 watts. Output transistor bias adjustment is included in circuit design. This allows for the modules to be adjustable for matched performance You can use this design to replace STK-0040(II),0050(II),0070(II),0025,0029,0039 Refer to the table showing all the possible types that these STK's can replace.  This design uses high Ft Onsemi KSC3503D/KSA1381E pre-drivers, MJE15032G/MJE15033G drivers Outputs transistors are specified as 150W Toshiba (2SA1943N/2SC5200N) or Onsemi (NJW0381G/NJW0302G) Since we use an integral heatsink, the parts is larger than the original but uses the same mounting holes The top of the heatsink is 15mm from the mounting holes and the HS is 96mm wide Heatsink is tapped for M3 x 0.5 screws, supplied Expected Performance: Total Harmonic Distortion: ~0.01% ( 20-20KHz,4-8 ohm, 31mA bias) Gain (based on Pioneer SX-780 design) = 15.5 (23.8 dB) Bias: Each emitter resistor in the SX-780 are 0.22ohm, that would be 0.22 *0.031A =7mV across each emitter R or 14mV across the two of them. Increasing the bias current will make the output transistors to run hotter. This lowers the crossover distortion and allows for a larger class "A" operating region. Reference: Google: "STK-0050 Replacement for SX-780 and others" @ Audiokarma web site for additional details on our design