Several things:

- As already posted you must NOT change the TX crystal. On JR radios 7channel plus radios, you can purchase pre-tuned TX "modules" that permit you to change the channels however.

- DO NOT attempt to change the TX channel by merely swapping out the crystal. Not only is it illegal, but you'll get reduced power output, and also cause sideband signals to be transmitted, that can shoot down other planes at your field.

- The crystals you found on Ebay are sold by various vendors. The OEM company that manufactures them DOES make them specifically for JR sets.
As such they CAN be used SAFELY on the receivers, provided you purchase the right set.

- There are sets of those crystals for the "single conversion" receivers which JR sells, such as the 6UL, and for the full range receivers. You must purchase the correct crystal!

- The crystal for say an R700 receiver is called "dual conversion JR" from that company... however IT IS NOT Dual conversion... and neither is the JR receiver! This is a misnomer, but it does help to identify which crystal goes with which receiver as the single/dual conversion conventions are used by other vendors.

- I've used those JR specific crystals extensively on various JR receivers w/o problems... I've also tested the results with a graphic frequency checker. They provide the same power output and performance as the original JR crystals.

- NORMALLY you cannot use crystals from other vendors this way. This particular vendor is an exception! They engineered their stuff specifically to suit replacing the OEM's crystals.