This is what I have built into Hameg's HM800 modules
AV8052 Service adapter
AV8073 Tone Burst Generator, similar to the one from 1973
AV8074 SQ quadraphonic encoder. Used for encoding decoded CD4 records and 4-channel tapes into SQ-signals that can be saved on an audio CD and played back via a SQ-decoder to get quadraphonic sound.
AV8077 Dual Low Pass Filter