I have this blog post you might be interested in;sites.google.comAnalog Electronics - High Stability OscillatorsThere has been a lot of interest in the Vackar oscillator lately because of recent (1968) articles describing its many merits. Although there hasn't been too much information on this circuit in the American magazines, a wealth of information has been published in the RSGB Bulletin. In addition,With modern components you can get down to very low drift rates. I am probably going to try a regen with the Seiler circuit mainly because I can keep the component count low better that way. Though the Vackar circuit is is very, very stable.