The lowest I have gone is 6 reps per set for heavier weights and up to 20 reps for lighter weights. I will often do a high number of sets when I use the pyramid method, ranging from 8 to 20 reps ...
Suppose that you want to gain muscle mass by using a pair of dumbbells which are NOT so challenging for you anymore. You could probably increase the resistance with heavier weights, but you train at ...
I am staying away from the "as-much-as-you-can". Now, in the dumbbells part of my workout I simply mimic a linear load progression at fixed number of reps, á la SL5x5. I just use smaller increments ...