In fact, this 1967 Electronic Design circuit generates two symmetrical ramps whose frequency depends on the values of the components used. Modern equivalent transistors can be used.
The circuit shown is a documentation on 80's tunnel diodes. The frequency depends on the delay line...
This circuit generates excellent sinusoidal signals and has the frequency adjusted by VR1 which is...
This circuit was adapted from an Italian publication that no longer exists. This is “Onda Quadra”...