Analog to digital converter (CB20538E)

This TTL circuit for PC was found in an English documentation from 1992. The integrated circuit used ZN426E is not in common today.

Multilayer Varistors for Surge Protection - TDK
TDK provides a wide range of EPCOS varistors for surge protection through Mouser Electronics....
Voltage Controlled Gain Amplifier (CB4898E)
This circuit provides a linear attenuation of a signal up to 100 dB. The circuit operates with...
Gain 100 Amplifier LM3900 (CB5043E)
As in the previous circuit (CB4052E), the relationship of values between the feedback and input...