Keithley 2601b single output variable bench dc power supply keithley 2601b p the keithley 2601b is a single output variable bench dc power supply sourcemeter smu instrument from the 2600b series this single channel smu instrument has a tightly integrated four quadrant design that allows it to simultaneously source and measure both voltage and current to boost productivity in applications ranging from r amp d to automated production test p p the 2601b has a 6 frac12 digit resolution an