it may affect loading of the crystal, so you may have to adjust the cap values used in your oscillator, but I've never had to do that with a TTL oscillator of the sort I previously described.

If you don't need to switch between crystals in a live circuit, then the 3-terminal header witha shorting plug to select which crystal oscillator you use will serve. However, it's better to have only one of the oscillators active at a time. Crystal sockets are a bit large and cumbersome, require a particular type of crystal package, and small, screw-machine-pinned sockets are not as reliable, for such purposes as one might hope.

A reasonable compromise might be to have a single TTL oscillator using a hex inverter, and a PAIR of 3-pin headers with two shorting plugs used to select which of two crystals is being used. The shorting plugs take the unused crystal out of the circuit entirely, so it has no effect on the characteristics of the oscillator when not in use.

RE