Armstrong's first regenerative receiver.
As the positive feedback (at 180 degrees at Wr) is increased, the amplifier will start to be an incipient oscillator.
I expect that the phase noise characteristics of ordinary oscillators (hartley etc) will then progressively apply along with the thermal noise at input of the amplifier.
However atmospheric noise from antenna on conventional AM frequencies will dominate.
Here is a tutorial about phase noise in oscillators and reciprocal mixing.
https://www.eecis.udel.edu/~vsaxena/courses/ece518/Handouts/Oscillator%20Phase%20Noise.pdfThe Q multiplier used on tube HF receivers was a similar application, however they were applied at the intermediate frequency.
The regen first stage and Q multiplier act to reduce the R component in the RLC tuned circuits to increase selectivity.
On Lafayette HE30 I used the Q multiplier setting of barely oscillating to resolve ssb.
That gave good fidelity however I no long use it on the digital modes because the Q mult is not stable enough. Replaced by xtal IF oscillators , Gilbert cell and ceramic filters.
An interesting experiment in analog domain would be a regen receiver, or Q multiplier locked to DDS.