We found this configuration in a 70s American documentation. The circuit makes use of operational amplifiers of the time. Modern equivalents can be tested.
This amplifier has a few Watt output, using old transistors. The speaker is 45 ohms, but with...
This circuit is from a 1965 Motorola manual. It can be implemented with a common 2N2646 and a 106...
This circuit, in addition to transforming a sinusoidal signal into a square, shifts its phase. The...