As far as I understand, there are several transformers in this box : one transformer with 1:5 ratio, to be plugged on a OTL headphones amp with "medium" voltage output (around 100V, what the RKV claims), and another one (in beetween 1:14 and 1:20) to be plugged on a regular speaker amp, as for these brave old SRD boxes.
I may be french, but there are simply too much words in some posts on this french forum to extract the exact meaning of all this
Ali