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A Battery Valve Regenerative Radio:The "Hergé".
The radio is called the "Hergé" as it looks a little like the radio used in Tintin "The Blue Lotus" by "Hergé. The Blog post here.
It uses low power cheap Russian Rod Pentode sub-miniature valves (Tubes or Pencil Tubes), the 1j18b.
The finalised design has a generous gain Audio Amplifier that can even drive a loudspeaker via a transformer and actually needs a volume control on stronger stations!
The finished Hergé radio (with reaction for volume)
The theory is that using a loop aerial as the tuning coil (with a feedback coil on it too) will remove the need for a separate aerial and earth. Also less local electrical noise will be received compare with a whip or long wire aerial.
The chassis is a piece of plywood (Hardboard or MDF will do too) mounted on battens deep enough to house PP3 battery. If you want C or D cell instead of AA cells for the "filament" supply (LT = Low Tension), then use taller battens.
My base is 26 x 17cm, but a bit wider would be fine.
The front panel is easiest to do neat if 2mm plastic sheet. But Aluminium or MDF can be used. Perspex / Acrylic is difficult to work without cracks. A disk type motorised tile cutter will cut Perspex or thin Aluminium sheets. My front panel is 12cm x 26cm x 2mm.
The coil / aerial is supported on two bits of panelling wood 41cm x 8cm x 9mm with the tongue and groove split off. This makes the coil "diameter" vary from 30cm to 42cm
The "cross" is supported a few cm above the base by a 3rd piece of panel board.
The 3 x 1.5V AA cell (with two dummy cells if only one valve) and the 4 x PP3 batteries are mounted on a plastic or wooden board screwed to the bottom. (was 8, but four is fine)
The valve is mounted on screw terminal block, though you can use veroboard/stripboard.
We'll call this 1 valve Regenerative Radio "The Hergé" in honour of his research and attention to detail. (fun stories too)
Hergé wrote that strip (in French) for the Belgian newspaper in 1934 or 1935 just after the Japanese invaded China and blew up the Manchurian Railway.
Tintin is picking up Japanese transmissions to/from spies in China in Morse.
Note DF loop aerial.
The Japanese lodged a protest with the Belgian Embassy after it was published!
It was later coloured and published in English as "The Blue Lotus". You can buy the full story in most bookshops and online.
The Hergé will be a one valve regenerative Radio running off batteries (3x PP3 = 22.5 / 27V, 6x PP3 = 45V/54V or 8 x PP3 = 60V/72V ). Optionally a second 1j18b can be added as an audio amplifier, especially valuable if you want to use 27V. You can even use 2 x PP3 (16V to 18V) if you add and amplifier. The valves (or Tubes) used are Russian Sub-Miniature Rod Pentodes made entirely for Military use.
See also VRAT magazine