Glorious Braun design of the best period : between the 1960s ascetism Braun was known for and the later gradual blurring of that "clear line" which can be seen in the Regie 540 for instance.
Although the Regie 510 may look flimsy, it still was a receiver in 1960s style : 17kg of metal and aluminium. With 2x 70W at 4 Ohm (20Hz...20Khz), it was also powerful enough to shake baby shake.
Braun's usual two-way volume is here : either a linear control (pushed in) or (pulled out) with a continuously variable loudness compensation added - quite effective.
Not much else to say : this represents the equilibrium point between one period and another, also available in silver fashion to choose which side of the equilibrium you prefer.
Better yet : this equilibrium costs very little today, overshadowed as it is by Braun's more austere efforts on one side of the timeline and the last Atelier series on the other end.
These images come from a luxurious Regie 510 french catalog ; the image with the liquid red background is from a lavish 40x60cm Braun 12-page magazine called "Live" published in 1974.