All HiFi / stereo amps made by Dynacord are ultra rare and I think the ST3 is the rarest one.

  The optical appeareance of this amp reminds on the Dynacord ST6 and Telewatt V120 or V117 mono tube amps (both EL84 push-pull), but with the cabinet laid down.

  Simple circuit. Just using a pair of ECL82 as driver / output tubes. The last two pictures show the version designed for radio consoles.