Triangular to sine-wave conversion using germanium point-contact diodes

The sine-wave generator is an essential tool for electronics education, indeed it plays a central part in demonstration and experiment. The conventional ‘audio signal generator’ found in most schools and colleges is, however, not always the most convenient instrument to use. How often has a student experiment lost its impact (and caused confusion) through the student having to change frequency range and then to track back across the whole range to start at the beginning, with all sense of continuity lost? And is it not an unwise teacher who puts together a demonstration of, say, resonance, without carefully selecting component values that put the frequency of interest somewhere near the centre of the decade range available for a continuous sweep?