I recall it being in Amateur Tape Recording magazine and if I recall correctly it was an FC Judd design. It's in a compilation book from ATR as well as a few other circuits.
My memory says it is a couple coils with diode bridge between them but any more detail than that I can not recall.
It should be here somewhere:
https://worldradiohistory.com/Archiv...cording-UK.htm
No idea which issue but suspect it is between 63 to end of publication.......