theres two types of clipping as youve probably figured out, current clipping where the transistor turns off completly, and voltage clipping where the transistor saturates, with a bjt the later cuases problems with storage time, wich is variable with temprature, hence makes for unstable HF oscillators. the later is better but is difficult to ensure this happens before the former with out some form of level feedback.
with jfet however either form of clipping isnt so bad, if you notice the circuit I put here there is a smal amount of positive gate current at clipping. but I just slapped those values together.
well not crystal overtones exactly, but frequency multipliyng oscilators, say to generate over 100Mhz - crystals tend to be difficult to get much higher than this even with 5th overtone.
you can still easily get nearly 2x full supplly swing accros the tank with a jfet. the resistor can also be replaced by an inductor getting you to exactly 2x supply.
For interest try putting the crystal across the inductor when it is tuned at the right frequency and see what happens, then see what difference it makes at different frequencies. Ive played about with a bag of10mhz crystals to find 2 that were precisly a some khz apart, eventually I made one lower by degrading by heating it with a soldering for some time, its to easy to seriously degrade it though.
unfortunatly most crystals are at a peak of frequency at room temperature, above and below this temp they start to fall in freq, untill you reach the higher flex in the tempcooef curve where the freq starts to rise again. this can be quite hot and the tempcoeef is then rather steep.
another trick is to look for crystals that will give you a correct frequency at overtone, 3,5,7th or use a frequency multiplier x2,x4 etc I spent ages doing this once. you can even go up in freq then divide by 1-256 with ttl etc. ofc a pll is the the other option.
The transistor capacitance changes with temperature, not to mention cheap ceramic caps too, god knows what the temp coef of breadboard cap is lol. not to mention anything other than air cored inductors. with a low capacitance transistor you would get better stability, with a lower inductance the transistor cap has less effect too. you can do a whole lot better than that with just the right parts.
I have a nice temp compensated oscillator wich I got with some other stuff but not a usefull frequency. unfortunatly a different crystal didnt match the temp comensation, but you can use capacitors wich have the opposite temp cooef. they also make trimmers like that too, although you can just put an ordinary trimmer in series with it.
last colpits I built was a wide range >2:1 1-2ghz VCO with a PHEMT (fet) this had an extremely low capacitance, but is probably a bit over the top for 10mhz. I had 2 wich I tried to keep 455khz apart, very difficult, they liked to sync up if they got closer than 1Mhz. (were a few threads about it.)
Colin =^.^=