This selectable constant current source was found in an English publication in 1983. The transistor can be the BD135 or the TIP31, which must be mounted on a heat radiator. The input voltage can be between 12 and 18 V. The switches select currents from 1 to 85 mA, but these values can be changed by changing the resistors. Operational amplifiers equivalent to the 741 can be tried out.
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