[Amps] 50 or 60 Hz, a problem?

[n7ioh]

    I have a friend that lives in Cyprus and he is looking for an amp.  
I was just wondering, I have seen transformers that say 50Hz and some 
that say 60Hz and some that say 50/60Hz.  I'm trying to help him find an 
amp and was wondering what difference there would be between the 50Hz 
and the 60Hz as far as operating them on a different Hz then what is 
stated on the equipment?  I'm not sure what they use in Cyprus, I am 
waiting to here back from him on that. 

                                    Thanks, Al, N7IOH