Some other devices have been made as SSB BFO adapter, and maybe, they are even better quality! One on ebay:

https://www.google.com/search?q=ssb+bfo+adapter&client=ubuntu&hs=prL&channel=fs&sxsrf=ALiCzsYD3kjseyP6ye_iEMVNs_LD8Tx5ng%3A1658990510851&ei=ri_iYsHKM9GtkwXNibfACw&ved=0ahUKEwjB2dag_Zr5AhXR1qQKHc3EDbgQ4dUDCA0&uact=5&oq=ssb+bfo+adapter&gs_lcp=Cgdnd3Mtd2l6EAMyBggAEB4QBzIECAAQHjoHCAAQHhCwA0oECEEYAUoECEYYAFDVBFjeCWDbDGgBcAB4AIABiQOIAcIGkgEHMS4zLjAuMZgBAKABAcgBAcABAQ&sclient=gws-wiz
Thank you very much for your advices. 
   Yes, I had seen that brazilian BFO 455 khz , in Italy sell it as well. I have asked before buying and the seller says that is not a product detector only an oscillator and it will not work wit that IF am output, only by proximity:
   https://www.ebay.es/itm/333941213623
He wrote me:
The function of this oscillator is create a slightly offset at 455 KHz signal to beat with a signal present in the internal stages of the receiver, thus transforming an SSB transmission into an AM.

Basically it is like when you are receiving an SSB signal in AM mode and someone transmits a carrier on the same channel: result is the SSB becomes intelligible.
To obtain this effect, you simply have to bring the wire that transmits the 455 KHz from oscillator closer to the antenna of the receiver and finely tune both controls (BFO tune and Radio tuning).