Chesson's BC Numbers File lists it as: BC-1421* Receiver, 100-156 MC, AM,CW Hazeltine, 11 tubes P/O RC-256-C It must have one of the very last BC- number assignments. I agree...it looks like some sort of enhanced BC-639, which had ten tubes. Maybe the eleventh tube is the rectifier for the internal power supply. Mike / KK5F