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Mystery Radio

Lost in the scramble of early radio design were a number of circuits whose sole purpose was to decrease the quantity of tubes necessary for adequate reception and reproduction.  The Reflex circuit and its sibling Inverse Duplex enjoyed wide popularity.  A few companies, like ERLA, David Grimes, and Acme Apparatus, were built upon the hope that these patents would carry them to long-term viability. 

The chart below, from the 1931 edition of Moyer and Wostrel’s Practical Radio Construction and Repairing tells the story best.

graph of popular circuits
As the cost and availability of vacuum tubes came down, the appeal of marginal, finicky circuits abated. Larger companies, like Crosley, were able to survive the passing of the Reflex circuit.  The slogan for their Trirdyn models was “Three Tubes Do the Work of Five.”   When the Reflex fad subsided, they had other patents to fall back on; ERLA wasn’t so lucky.

 

According to Alan Douglas in his Radio Manufacturers of the 1920’s, George Pearson decided to go into the radio business “in the fall of 1921.”  By 1924, his Electrical Research Labs, or ERLA, had ads in all the major radio magazines promoting a complete line of beautiful components, all designed to serve the hobbyist who wanted to build their own Reflex set.  Articles on the ERLA Reflex circuit were in virtually every new radio publication on the market.

Erla Logo erla selectoformer

semi-fixed crystal detector

ERLA semi-fixed
crystal detector
erla tube socket
 
erla 1 tube schematic
Erla 3tube schematic

 

By 1926, ERLA’s only presence was in the form of little spots (like the one on the right) buried in the back pages.  In September of 1928, Pearson sold the name and got out of the radio business

 

small text-only ad

Sometime between 1924 and 1926, Pearson also built a line of radios carrying his own name (under the ERLA banner.)  One of my favorite radios in the Museum comes from this era.  Outwardly plain and unassuming, the interior reveals the company’s strengths and weaknesses: beautiful components that delivered marginal performance. 

Interior of Pearson model 5TAS-20
inside view of radio

Perhaps the most intriguing aspect of this particular set is the choice of circuit: Jackson Pressley’s version of a Superheterodyne, straight out of the 1926 edition of the Radio News Superheterodyne Book.
   
Trimmers C3, C4, and C5 were manufactured by St. James. 
Otherwise, all other components are branded ERLA.

 

   
Volunteers John Bravis and Jon Lieberg with Pearson 5TAS-20

After volunteer John Bravis traced it out and confirmed that it was indeed a Superheterodyne, we were surprised to discover that the IF stages responded best between 240 and 270 kc (kHz) while the oscillator ran 240 kc above the incoming signal.

We were expecting the usual 30 to 100 kc of the time, but since the specialty of St. James Superheterodyne kits was their 240 kc IF coils, it would appear that this was a cooperative effort between the two companies.  Unfortunately, ERLA chose to use RF coils with rather broad response for the IF stages, leading to poor performance. 

Superheterodyne kits abounded in 1925 and ‘26, but this set looks too good to have been a built outside of a factory.  To market a pre-built Superheterodyne in 1926 was risky at best; Westinghouse attorneys would have been all over anyone who tried.  We can find no advertising of or reference to this model anywhere.  Even Alan Douglas has never heard of it.  We would love to find out more.

In spite of ERLA’s short-lived success, George Pearson was a significant contributor to the art of the individual component, a concept that is all but lost today. 
                                                                                     SNR

 

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