This shield circuit is from a 1968s Motorola documentation. The relay is according to the supply voltage. R1 can be reduced to lower trigger voltages.
This conventional circuit with a source adjustable to 1.5 A was obtained in a documentation...
With this circuit it is possible to compare the values of two capacitors in the range of 100pF to...
We found this configuration in a French documentation from the 70s. It appears sometimes in this...