This circuit was obtained from a 90s Radio Electronics. The value of R1 determines the scale according to the table next to the diagram. The power suppley must be symmetrical.
This circuit is recommended for alarm systems since it has a good output stage. The circuit is...
) Suggested by Philips in a 1968 documentation this circuit has very high 10 ohm on-load voltage...
No information is given about the transformers in this circuit suggested by Motorola in a 1968...