This circuit was found in a 1966 General Electric documentation. The circuit makes use of PUTs that are uncommon components today. Counting direction depends on the programming in A and B.
The circuit presented was found in the 1994 National Instruments Linear Applications Handbook and...
The operational amplifier for this tone control found in a 1977 Signetics manual may be the 741....
This circuit is based on an LM3900 transconductance operational amplifier, found in 1992...