The one I currently have was very unstable until I found and corrected the
problem - the low frequency (1750-2000 kc) coil for the tank circuit had
several loose turns on the grid end, where the coil dope had dried out.
Tightening up the wrap of the coil and sealing the turns with some epoxy has
resulted in a very stable oscillator. Its still kind of sensitive to
mechanical shock, so don't bang on it, but once it's set, it stays!

Chris Bowne, AJ1G
Stonington,CT