We found this circuit in a 1966 General Electric SCR manual. The circuit can be implemented with modern SCRs.
Other operational amplifiers of the same series can be used on this circuit found in Motorola's Linear...
Found in 1980s documentation, this circuit produces 1 Hz flashes. The op amp supports equivalent. R5...
In the figure we have the way to use a single control voltage to act on two varicaps...