prove it's a 'good' circuit, which it probably isn't anyway.
Advantanges: Superior frequency stability. Less phase noise. Very stable RF amplitude due to the self-regulating Class C bias. Superior to a Colpitts oscillator for VFO applications, because the self-bias allows accommodation of frequency-dependent loop gain. Superior to Hartley oscillator because less spurious frequencies, because single Inductor. Reliable. Simple to construct. This is a favoured choice for signal generators and transmitters.
What has class C got to do with it?.
Because this thread has been primarily about: "where does the reverse-bias for the varicap come from, if it's not
self-biased in Class C?"
Sounds a fine definition to me,
Definition of Class C agreed. Good. Found some common ground
and proves that the oscillator isn't class C. <..> not going to be class C as it doesn't meet your 1942 definition, or my more universal one.
Denying the evidence of Class C operation doesn't make it 'go away'....
Exhibit 1: Id=0.6 mA = Class C
Exhibit 2: Reports of Negative Gate voltage = Class C
Exhibit 3: Data from Denver University
Electronics 16 = Class C
How much more evidence of Class C is required?
Class A amplifers don't usually get hot, which almost all (if not all) sinewave oscillators are - you certainly don't want them hot, for stability reasons.
Class C Oscillators
"class c oscillator" - Google Search operate in Class C, and this is what makes them run colder than Class A oscillators. Because Class C means: 'biased beyond cutoff', is where the varicap gets its reverse bias.
Here is some analysis of this Clapp "Class C oscillator":
https://www.electro-tech-online.com/custompdfs/2009/07/322Lecture24.pdf
Conclusion: The OP circuit contains an example of an oscillator which
stabilises in Class C. For a few cycles during start-up, the circuit operates in Class A. Stable Class C operation in oscillators provides advantages over Class-A biased oscillators.
And of course... because the j-fet is biased beyond cutoff, means a negative voltage is present on the gate. It's enough to bias a varicap, connected with 'pointed end' to ground. [edit]
That's it, I've had quite enough of this 'Class C' and 'varicap bias' thread now.