I just listed a Collins F500Z5 Mechanical Filter that I understand is used for for 618T or PRC47 radios. I have a bunch of other crystals and sockets etc. for Collins radios listed on eBay this week. Thanks for taking a look & 73 - Bry, AF4K http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110930374951