AMRAD Model 81 ("Bel Canto" Series) Receiver
Radio Service Data Sheet
June 1930 Radio-Craft

June 1930 Radio-Craft

[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

These images of an AMRAD model 81 "Bel Canto" radio images retrieved from eBay.

AMRAD Radio: A Brief Overview and Historical Context

Amrad, American Radio & Research Corporation, was based in Medford Hillside, Massachusetts and was founded in 1915 with funds from J. Pierpont Morgan. The company's first manager, Harold James Power, was an amateur radio enthusiast and built a research laboratory. In 1916, Amrad made its first broadcast to J. Pierpont Morgan Jr., who was aboard the ocean liner "Philadelphia."

Amrad received orders for military radio equipment during World War I, but discontinued these orders after the war ended. To keep the company afloat, Amrad produced items such as electric egg beaters and cigar lighters. In 1919, Amrad was awarded a contract to make 400 SE1420 receivers, and it began advertising components for amateur radio enthusiasts. Amrad's crystal set was a popular product and helped the company during difficult times.

In 1923, the company joined the Independent Radio Manufacturers Inc. and acquired the rights to the Hazeltine neutrodyne invention. However, Amrad went into receivership in April 1925 and was purchased by Crosley Radio Corp. for $39,000. Amrad also made gaseous rectifier tubes, including the S tube developed by Charles Grover Smith, which was used for transmitter voltage. Amrad's patents for the gaseous rectifier tubes were eventually sold to Raytheon.

AMRAD Model 81 ("Bel Canto" Series) Receiver

The AMRAD Model 81 chassis is fused at three amperes. The "antenna compensating control" is the 10-plate variable condenser marked CIA; while while the remaining trimming condensers are adjustable, through the shield can, with a screwdriver. Binding posts at the rear of the chassis permit selection of the correct tap on the antenna input inductance L1 , for the required degree of selectivity and sensitivity. When the tube is renewed at V4, it will probably be necessary to readjust the setting of R8. If circuit oscillation should appear in the receiver, it may usually be traced to a defective '24 tube, which should be replaced. The cord which operates the tuning dial is kept in tension by an adjustment which compensates for stretching; this is regulated by putting a screwdriver through a hole cut in the edge of the dial drum. Each of the R. F. transformer primaries (Ll1, as well as P in L2, L3 and L4) consists of a winding of about 200 turns on a bobbin at the grid end of the secondary; it has a direct-current resistance of about 80 ohms.

The metal placard shown in the eBay radio image reads as follows:

"Licensed only for radio amateur experimental broadcast uses and for electric phonograph reproductions from grooved records. Licensed for use in connection with electric phonograph devices sold or manufactured and sold under license from Radio corporation of America. Except as in their license notice expressly provided the sale of this apparatus confers no license under any any of the foregoing patents or under any other patents under which Radio Corporation of America may have the right to grant licenses to make use or sell any other with resect to broadcast reception and electric phonograph uses licensed only for private use in homes and for entertainment and educational purposes otherwise than in combination or in connection with apparatus in the field of wire telephony or apparatus for projection or production either directly or by electric currents waves or impulses of still or motion pictures. Licensed in Hazeltine and Latour Patents Issued and Pending."

Posted February 9, 2023

Radio Service Data Sheets

These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers. There are 227 Radio Service Data Sheets as of December 28, 2020.

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AMRAD Model 81 ("Bel Canto" Series) ReceiverRadio Service Data Sheet June 1930 Radio-Craft

AMRAD Model 81 ("Bel Canto" Series) Receiver
Radio Service Data Sheet
June 1930 Radio-Craft