This circuit is from an1966 General Electric documentation. The Triac can be equivalent to 6 A or more, mounted on a good heatsink. Any diac can be used.
We found this circuit in an old publication. The circuit can be implemented with modern equivalent...
Operational amplifiers used in this 80's circuit is not very common today, but the setting can be...
No information is given about the transformers in this circuit suggested by Motorola in a 1968...