There is am ebay listing for 'MACHLETT 3-500ZG', new, with warranty etc... - http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160543625478 Who is MACHLETT at all, I never heard of them. The only sources for 3-500 tubes I know are either expensive and old Eimac or 'good Chinese' tubes from RF Parts... Alex K2BB, in need of a pair of 3-500's