The Experimental Radio Project

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TRF radio schematic
The schematic. Click on the picture for larger version.
Not the greatest feat of engineering in the world, but it works well for such a simple radio, and even picks up some shortwave at night!

A technician friend pointed out that it appears the RF Gain control can short out the battery. Not really, there is a 1K resistor ahead of the control. With the control set to 0 ohms I did not see the battery voltage drop at all. With the volume control set to minimum, the set draws 6 mA of current. Setting the RF gain control to 0 ohms causes the current draw to increase to 12 mA. At full volume the set draws 50+ milliamps. Since the listener would never turn the RF Gain control to 0, this seemed acceptable.

Tandem Tuner
So what happened to the cool TANDEM TUNER?
Tandem Tuner
I still have the coils
I removed the TANDEM TUNER before I got the RF amp working. In the future I'll wire it back up and see how it works.

Tuning a 1924 radio
 Now you may ask yourself "Why would anybody want to turn all those knobs to tune in a radio station?"
Well first of all, it's fun! Secondly, radios from the early 1920's actually had a lot of knobs.
This factory made one has six. (and no speaker!)
American Marconi model 106
This American Marconi model 106 from 1918 has seven knobs and two adjustable crystal detectors, just to TUNE the radio.
There is no amplification of any kind. This one is worth over $20,000.

 FYI - The American Marconi Company was controlled by the British Marconi Company. In the interest of national security, a new
U.S. company was formed in 1919 to buy out the British interests. Almost all of the financial, capital, technical and human assets
were transferred from American Marconi Company to the newly formed company, the Radio Corporation of America. (RCA).


This concludes our broadcasting day.