The tranny is a very exotic volume control, it has a hidden part, which is called an auto former
An auto-former is like a choke and a transformer:
She is the best of both worlds and the auto-former is built on a seductive HY Nickle Core
Like a choke, the auto former has a single winding, but the auto-former has several taps to attenuate the signal in 32 steps. Like a transformer, the auto-former has a core, but it doesn’t pass the signal through the core from the primary to the secondary.
Some consider the Auto Former superior to resistor based volume controls or attenuators because they don’t attenuate the signal through heat loss.
If u are wondering which is better a transformer volume control or auto former volume control just read this thread
same dynamics to be heard at all levels - it is so utterly
transparent
The middle switch is a three input selector switch
Rather than using a single switch, two discrete switches are used to control the level. The switch on the left has 12 positions that are in 3.75dB increments. The switches in the middle have 3 positions allowing +1.25dB, 0dB and -1.25dB modification of the overall level. By using this dual switch arrangement 1.25dB steps are possible. The total attenuation range goes from +1.25dB to -41.25 dB in 32 steps. The nature of the device skips the -3.75dB tap so the steps are +1.25, 0, -1.25, -2.5, -5, -6.25, -7.5. 1.25db steps to -41.25 and off.
This is the only manually controlled auto former based volume control being currently produced