Marshall JCM900 Preamp Schematic

I did not include technical data for this preamp, it's just a scheme to guide repair. May be useful for those who have a Marshall JCM900 guitar preamp .

10w 6L6 Push Pull Amplifier

Schematic

Frequency Response :
15-65Kc (-3dB), 1Kc input, at 3W RMS output across 16 ohms.

Power :
10W RMS for 700mV RMS input, with a THD+Noise of 0.29%

Tube Complement :
1x 6J5 (input), 1x 6SN7 (differential phase inverter), 2x 6L6GC (output), 1x 5R4GYB (rectifier)

The Output Transformer :
The Hammond 1650K is a 7 lb. oversized monster for our current and wattage demands, but it has a 3.4k primary.