As Scott said, any amplifier with gain can be used. Generally, oscillators
do not work over infinite frequency range. If you wanted to check out the
low frequency surplus crystals, you built one with a lot more inductance in
the "plate" lead. Most hf crystals will check out fine in a single
oscillator.

I have built some using an fet for gain and a led to indicate current flow.
Although I have some with meters, generally you are looking for a go / no-go
type of indication. Heath grid dip meter works well, but you need to build
a socket adapter.

I built a single fet gate dip meter using an MPF-102 out of the Handbook. I
used an FT-243 crystal socket for the coil. It works great as a crystal
tester and the meter indicates activity. Great to let me know I have a
dirty crystal. Although it does not work on low frequency crystals, it
works well otherwise.

My favorite is one from Ham Radio. It was a solid state oscillator with an
isolating amp for the counter. It has a built in switched capacitors for
change crystal loads and if you plug in an inductor, it will read out in
inductance. I made adapters for various types of crystal sockets.

It reads overtone crystals quite well.

The big problem is sorting out the drawers full of crystals. The
mathematical odds that you will have and can find just the crystal you need
decreases as the number of crystals increases.

Colin K7FM