UPDATE 2/27/17 This radio is a vacuum tube regenerative (called valve in the rest of the world). It covers the AM broadcast band, as constructed, from about 600-1200KHz. It is a rebuild of a radio I packed into a small metal case that never quite worked. Now is it very good.
The schematic is to be found online by searching <One tube 12 volt space charge radio circuit>by Norman Leal.
It uses a space charge tube which were used in automobile radios in the late ’60’s and early ’70’s. Although the tube uses 12 volts dc it draws one half amp so it requires a 12 VDC, 750 ma power supply (wall wart type works fine). It likes my antenna: a loop of insulated wire, eleven turns with a loop diameter of eight inches. One end of the loop connects to the radio with a lead wire so the loop is elevated and the other end is not connected to anything. –>Presently I am using a 36 inch wire and the radio works well.
Advice. One turn of wire 1/4 inch above the coil wrapped on the coil form is enough for the “tickler” coil. The resistor listed as 4.7 Megohms was not effective and I used 9 Megohms with success. If you want to run an amplified speaker (LM 386 for example) take one lead from any ground point and the other from the NON powered input to the transformer. The radio can put out good volume with headphones or an amped speaker. The transformer is 2000:8 ratio.
I added a 100UF and 0.1uF capacitors to the 12 volt power connection.
Where to get tubes??? Radio Daze, Tube Depot, Antique Radio Supply in the U.S.
If I were young and it was 1960, I would be listening to great Rock ‘n Roll at night under the glow of the electron tube!
This is a regenerative radio (1920’s tech that works very well) that uses a ceramic resonator instead of a coil for the tank circuit. The design is from Peter Parker, VK3YE. It works well, but has a very narrow frequency range on the 40 meter band. The narrow frequency with a variable capacitor with a range of 16-116 pF provides great selectivity although some areas of the tuning range are dead.
A tank circuit is a combination coil and variable capacitor in parallel near or directly connected to the antenna that selects one frequency and excludes others as the variable capacitor it turned (“tuned”).
6/5/16: I added a switch and another ceramic resonator of a higher frequency and now have a 120 KHz tuning range (~40 KHz overlap).
Some more: A 40 meter receiver (G3XBM), a 1920’s look solid state regenerative for shortwave which uses three variable capacitors, and an AM broadcast band tube radio.