This circuit was found in an Electronic Design from the 90's. It makes use of components from the time. Triac is according to the controlled load.
The original document is from Philips, but now available from NXP (www.nxp.com) which is the...
In the figure we show how to implement a voltage-controlled oscillator. The circuit is from Texas...
Three LM158, LM258, LM358, or LM2904 operational amplifiers are used in this instrumentation amplifier....