Modern Radio Labs®
HB-2 shows how to build both the #2 2-dial set and the #2-A single dial set. They are the same circuit but the different types of condensers make a different panel and wiring layout.
The MRL® No. 2/2A is a two circuit (“dual tuned”) design, with a series tuned primary (“antenna ground circuit”), and a parallel tuned secondary (“tank” or detector circuit), in a single autotransformer coil. In tandem with the separate control of the variable capacitor connected to ground, the detector is tapped at the top of the coil, and near the bottom (closer to ground), to impedance match the detector for varied selectivity and sensitivity.
The series-parallel variable capacitor arrangement and the detector tap in this circuit is historically significant. Elmer Osterhoudt is one of the very first, if not the first writer/designer ("guru of the past") to experimentally impedance match the detector in a crystal set circuit. In addition, he is by all accounts, the very first to apply a series/parallel capacitor arrangement to a single coil.
In actuality, the design of variable detector tap is present in a couple of early circuits originating back to the turn of the century (1900), but in the very early days of radio, as one editor wrote in 1927: “...little attention, if any, was paid to the subject of matching impedance”.
The MRL® 2/2A is the very first professionally developed “High-performance Crystal Set” of the 20th Century, in the 1930's, during a period of commercial emphasis and development of tube technology for radio.
Copyright Paul L. Nelson 2023
1. Introduction 2. Building the set 3. The Antenna System 4. Operations and Testing 5. Theory of Circuit 6. Records by Location
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This MRL® Handbook is included with our MRL® No 2xpn Crystal Radio Kit