This circuit is from a 60's documentation. The circuit uses components from the era and serves to monitor a 150V continuous power line.
September 2017 - STMicroelectronics STBR3012-Y high voltage rectifier for automotive use is in...
This configuration enables the use of low current switches or sensors to control high power loads...
I found this circuit on a December 1976 Radio Elettronica. The Italian magazine no longer exists, but...