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The Armstrong Regenerative Patent

The dominant property at the dawn of the Broadcast Era was Edwin Howard Armstrong’s 1914 “Wireless Receiving System” patent number 1,113,149, commonly known as the Armstrong regenerative patent.  It turned a barely adequate single-tube receiver into a world-beater, dramatically improving both sensitivity and selectivity. 

The December 2010 issue of the Pavek Museum of Broadcasting newsletter identified a distinct set of companies who were manufacturing wireless equipment before, during, and after WWI.   This group included Adams-Morgan, AMRAD, Clapp-Eastham, De Forest, Federal Telephone and Telegraph, General Electric, Grebe, Murdock, Western Electric, Westinghouse, and Wireless Specialty Apparatus (owned by United Fruit). The smaller companies within the group who had the foresight to purchase rights to use Armstrong’s regenerative patent for the short time that it was available in 1920 held a distinct advantage over those who did not.  The four largest companies, General Electric, Westinghouse, United Fruit, and Western Electric eventually became “partners” in the newly formed Radio Corporation, controlling all of Armstrong’s pre-1920 patents.

Edwin H. Armstrong
Edwin H. Armstrong

Although the familiar regenerative circuit looks like the image on the right, Armstrong’s original designs were considerably different. His 1913 patent application had six different drawings, none of which had a plate circuit coil (tickler) inductively-coupled to the grid coil, and interestingly, none had a D.C. path to ground from the grid. The lack of a D.C. grid return caused a myriad of instability and hum problems. Neither Armstrong nor Lee de Forest was able to solve the mystery of grid-bias. That was left to the genius of Fritz Lowenstein, who applied for his “C-Bias” patent in 1912, but didn't’t receive it until 1917. In the meantime, Armstrong’s designs were captives of the still untamed Audion. 


1 tube regen

 

The drawing on the left is the first of six in the patent application.  Whatever his intention, it’s clear that Armstrong was building an oscillator here.  He set up resonance in virtually every component; even the inductance of the headphones (R) played a role; how he applied it determined the function of this circuit.  The transfer of energy from the plate circuit back to the grid circuit occurs at point “O” on this schematic. The ground connection at “G-2” is an attempt to stabilize the tube.  

The arrangement of the coils in Figure 3 of the patent application (below left) is virtually identical to those of the 1916 Adams-Morgan Paragon RA-6 and nearly the same as the 1920 Grebe CR-3 .  

from Radio Manufacturers of the 1920s by Alan Douglas:
“By 1920 Howard Armstrong’s legal expenses were mounting, while he waited for one of the large electrical or wireless companies to make an offer for his regeneration and superheterodyne patents and applications.  His attorneys hit on the idea of licensing the myriad makers of regenerative receivers for the amateur market, under his patent 1,113,149 (1914), for a royalty of 5% of sales price, and were soon signing them up as fast as they could spot their magazine ads.  Since the ham market was considered negligibly small, issuing these licenses would not endanger the eventual sale of the patents to commercial interests. 

The following companies were licensed, more or less in the order listed: 
American Marconi (only for one or two stations)
International Radio Telegraph Company
Adams-Morgan Company
Clapp-Eastham (4/18/20)
A.H. Grebe  Co. (4/30/20)
Chicago Radio Labs (5/15/20) (became Zenith in 1923)
Precision Equipment (later purchased by Crosley)
Cutting & Washington (7/7/20) (became Colonial in 1924)
Jones Radio (affiliated with Kellogg)
Mignon
Tri-City Electric
(built radios for Montgomery Ward)
Klitzen (affiliated with Michigan)
The Radio Shop
Oard Radio Laboratories
Pennsylvania Wireless
The C.D. Tuska Co.
Radio-Craft
(later purchased by De Forest)
Colin B. Kennedy
Eastern Radio Co.

Chelsea Radio

 



All of these companies, but the first two, were small; indeed, some were nothing more than high-school boys working in their attics.”1
It soon became apparent that their Armstrong patent rights were, for many of them, their greatest asset. 

After Westinghouse purchased Armstrong’s regenerative and superheterodyne patents in November of 1920, licenses were no longer available. Westinghouse joined the RCA monopoly and opportunities seemingly evaporated for the small manufacturer until, as providence would have it, the need for neutralization in early vacuum tubes, and RCA’s refusal to bargain with Hazeltine (the holder of neutralization patents) forced the doors of opportunity wide open, once again, for another group of small American radio companies who joined forces to form the IRM (Independent Radio Manufacturers) and purchase the rights to build Neutrodyne receivers.

2011 S. N. Raymer   

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1 Radio Manufacturers of the 1920s
by Alan Douglas, vol 1, pg vi