Hi there, that info was released by Yeasu quite a few years ago, there is no update now, somewhere there is a 4M pre-amp available for the 847 along with details of how to modify the bandpass filters to allow much higher power out and drastically reduce the current taken when on 4M, both my 847's are fitted with the preamps and filters modified, have not seen the mod mentioned since.
Leighton. GW3FSP.
gw3fsp