Carvin Quad-X Amp
There are four channels in the Quad X: Clean 1, Clean 2, Crunch ,and Sustain. There are a total of nine 12AX7 preamp tubes used.
It's called "Tube Cascade™" - The Quad X uses 9 tubes.
Each 12AX7 tube has two sides: Clean channels 1 & 2 use a single tube stage - each taking a side from tube #1 (V1). Channel 3 uses 2 tubes which is 5 tube stages (V2, V3, and half of V4). Channel 4 uses 11 tube stages - the other half of V4 plus 5 more tubes (V5, V6, V7, V8 and V9).
Front/Rear Panel details
Features include mono or stereo operation, 6 flexible effects loops, a spring reverb tank, a first-rate adjustable noise gate, cabinet-voicing simulator circuitry for direct-in, and a 5-band graphic EQ in addition to each channel's dedicated active EQ knobs.
The FS-77 footswitch controls the preamp's channel selection and reverb, effects loop and graphic EQ for each channel.
Below is a shot of the inside of the Quad-X. The tubes designated V1-V9 and go from left to right.
Here's an advertisement from 1992.