How to tell the brand of crystal
I bought a junk box of airplane equipment at an auction and have several crystals in it. The estate had several brands of radios and receivers on the auction as well, so there's no telling what brand of crystals I have. Some of them have a yellow cap with the channel on it, but that is all I can tell at the moment. Are there markings on the crystals that will tell me who manufactured them. I would like to know so I can either sell them or put them to use.
Thanks