This scheme looks impossible because there is no base bias. But it works !
I checked it in the band 450 KHz - 28 MHz.
C1/C2 =4 ÷ 5.
R1=10 ÷ 60 KOm. Controls regeneration level and filter quality.
V1=3 ÷ 6 V.
Q1 - BFP719, 2SC633. But really it was our КТ315 А-Г.
For 450 KHz, C1=1000 pF, C2=200 pF. L1 from transistor receiver for this frequency.
For 28 MHz, C1=100 pF, C2=24 pF. L1 from input circuit of transistor receiver. Consists from 8 turns of electric wire on plastic tube 8 mm diameter. With the ferrite string.
Filtering is about 20 KHz.
This is collector grounded scheme and big resistor in emitter circuit creates very great stability.
The output signal in Q1 .The resistor tuning is very soft. If you overtake generation level, it becomes a very stable sinusoidal generator.
This special base connecting of Q1 works as a detector (with R2=10K,C4=10000 pF LPF filter) of simplest AM receiver with a small antenna in bas