This circuit was found in a 1969 Mullard documentation. Used transistors can be replaced with modern equivalents. Output transistors may be BD135 and 136 with heatsinks.
This circuit is from 1976 documentation. It uses the operational amplifier 709 which is no longer...
This circuit was found in a 1996 documentation. It is a photometer with a logarithmic scale of...
This circuit for the very low frequency range was found in the Radio Electronics magazine of...