Note
QST, Oct 1938, p. 127.
QST, Nov 1938, p. 127.
QST, Dec 1938, p. 107.
Available in two combinations including with either the DB-20 (as the DB-20-70) or the 510X (as the 510X-70).
QST, Feb 1939, p. 127. (Details)
QST, Apr 1939, p. 127. (Details)
QST, May 1939, p. 127. (Details)
Brief review. Radio, Jan 1939, p. 31.