PWM/PPM with external carrier
Just to play around, drew up a potentially relevant triangle generator, that includes two of the subcircuits in the Dennis Feucht EE-times-article / book-excerpt linked in the comment above. I have not built this, don't know how far it can go with discrete components, and likely needs some changes. (I am happy to hear if there are fatal flaws and/or what needs to be fixed!).

One current into a resistor controls amplitude. Another current into a capacitor controls ramp rate. Frequency is controlled by ratio of the two currents. Voltage input controls level (should be buffered coming in). The delay introduced by the comparators and logic is expected to make amplitude control imperfect. Diodes something like BAS40 or BAS70?
Here is a Falstad simulation also for conceptual illustration (not a serious simulation). Has sliders on right hand side adjust the three inputs.
Also, following up a note in the same book excerpt, a more elaborate version of the current-switcher subcircuit is found in the left side of the &quot;equivalent schematic&quot; diagram of this old NE566 datasheet