This filter configuration used in telecommunications uses 4 Jaumnann crystals that are interesting for low and medium frequencies. The circuit is from an 80's documentation.
This source was found in Philips' 60s documentation. The transistors are from the era and the...
This circuit is the digital indicator for the previous circuit and can be used with similar...
Found in a 90s Electronic Design, this circuit operates with Maxim components of the time. The...