The yellowed diagram was traced in 1974. Heavy graphite lines mapping the heart of the Neve 1272 bus amplifier.
Where the secondary of the 10468 input transformer connects. T First Stage Gain Tie a resistor here to ground (B-) to boost gain. K Second Stage Gain Neve 1272 Schematic
If you are looking at a schematic online, you might see handwritten notes. Common modifications include: The yellowed diagram was traced in 1974