Radio, May 1938, p. 93
Model 21AA – 9.5 to 550 meters, $139.00
Model 21MA – 9.5 t0 3750 meters, $155.00
E. M. Sargent's Model 21 receiver used 12 metal tubes and had a regenerative RF stage. The amateur band 21-AA tuned 0.55 to 30 MHz, while the commercial 21-MA covered from 80 kHz to 30 MHz.
