This amplifier was found in a 1970s documentation. Darlington transistors can be replaced for modern equivalents of at least 80 V x 2 A, equipped with good heat sinks.
This circuit is from a 1975 Motorola manual. The FET can be the BF245 and the output voltage...
We found this circuit in a 1980 documentation. With basic changes, including transistors that were...
This circuit not only indicates when the battery is on but also when it is low. The circuit is...