Hello. I was hoping someone could clarify something in these schematics. R38 is listed as 1K ohms in one of them(version b), one says 120V?(version E), and the original says 1.6k. Then there is a version someone made with R38 at 150ohms. I would like to use version E in my restoration. Both boards had a 200 ohm installed. Thank you in advance for any help.
I answered your question in the conversation you started with me. I will answer it again here for everybody else to see and maybe get some other opinions. The original NINE uses a trimmer to adjust the current into a 4 Ohm load. The trimmer starts out at full resistance and then adjusted until the amplifier puts out 120W into 4 Ohms as the input to the amplifier is increased. With the trimmer at full resistance the amplifier will clip well before 120W is reached. The NINE+ uses a fixed resistor for this, I use a 220 Ohm 3W. This resistance allows for a bit over 120W into 4 Ohms. The bias trimmers are set evenly for 1A across one of the PCB mounted fuse holders with no input. Monitor this current until the heatsinks reach equilibrium and adjust accordingly. Heatsinks will be hot.
The NINE+ used 2SD555 output transistors, different output transistors may require a different resistor value. 220 Ohms works OK for MJ21194G outputs in my experience. Fortunately the resistor is fairly easy to get to if replacement is needed.
Craig
The NINE+ used 2SD555 output transistors, different output transistors may require a different resistor value. 220 Ohms works OK for MJ21194G outputs in my experience. Fortunately the resistor is fairly easy to get to if replacement is needed.
Craig