[Radio Wrangler]

Most semiconductor makers pepper their datasheets with weasley words like "We have a policy of continued product improvement and specifications are liable to be changed without notice. So there. Yah boo sucks!"

Consequently, the seasoned designer (= well bitten) knows to apply thorough damping, knowing that future years will bring much more frolicsome devices.

Once upon a long time ago, there was a little oscillator chip called MC1648. It was part of Motorola's MECL III logic series. It could go up to about 200MHz and got used in all sorts of things. Motorola improved their processing for later MECL families, but kept the old 1648 on. It performed a valuable function. It may have had a few die shrinks along the way. The bipolar transistors making up the 1648 became much livelier. and later production parts fitted to old PCBs started to think the old resonator tanks looked like decouplers, and that the tracks to the tanks looked like much more interesting resonators. Result: oscillation at a frequency set by the track lengths! People started desperately seeking old stocks of MC1648s, ones which were not so fruity.

Valves got improved a little over time, but by nothing like the factors semiconductors got hit by.

David