One Tube Regenerative Radio Circuit


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A regenerative radio works by feeding back a small amount of amplified output of the detector back into the input. Thus it achieves sensitivity far beyond what only a detector could alone. This simple regen radio uses a single tube as it's detector and amplifier; the "Audion". It's a great first project for those wishing to bring back some nostalgia by building one of the first amplified radio sets. Built on a board using point to point wiring and a set of period headphones, it can be a great functional conversation piece.

Schematic

Schematic for the One Tube Regenerative Radio Circuit

Parts

Part
Total Qty.
Description
Substitutions
R1150K Linear Taper Pot
R212.2 Meg 1/4W Resistor
R3110K 1/4W Resistor
C11250pF 100V Ceramic Disc Capacitor
C21365pF Air Variable Tuning Capacitor
C3, C42120pF 100V Ceramic Disc Capacitor
C510.1uF 100V Ceramic Disc Capacitor
V113A4 Audion Tube3S4, 3Q4 (See Notes)
L1130 Turns 26 AWG Magnet Wire (See Notes)
L2180 Turns 26 AWG Magnet Wire (See Notes)
L3120 Turns 26 AWG Magnet Wire (See Notes)
S11SPST Switch
HEADPHONE1High Impedance Headphones (2K or Greater)
ANT1, ANT22See Notes
MISC1Board, Wire, Sockets For V1, Case, Knob for R1, Clips for Antenna and Batteries

Notes

  1. L1 - L3 are constructed on the same coil form. A toilet paper tube will be the coil form. Secure the 26 AWG wire to the form by punching two holes close together and winding the wire once around the "bridge" between them. Alternately, just a drop of hot glue can be used. Leave about 6" of wire. Wind on twenty turns close together but never overlapping. Make a tap by securing the wire with a drop of glue and twisting a loop. This is L3. Wind 80 more turns in the same direction and then secure the end, leaving about 6" of wire at the end. This is L2. Now secure the 26 AWG wire 1/8" from the end of L2 and wind 30 turns in the same direction as the other coils, making sure that this coil is spaced 1/8" evenly from L2. Secure the end and leave about 6" lead. This is coil L1. Now trim the extra length of the coil form and spray the coil with several coats of lacquer to hold the wires in place.
  2. R1 and S1 can be one unit if you purchase a pot with a built in switch. This will avoid turning the set on with full regen and causing a nasty squeal from the headphones.
  3. The 3S4 or 3Q4 can be substituted for the 3A4 in the connections of pin 3 and pin 4 are swapped.
  4. An antenna of only a few feet can be used for ANT1 for easy indoor installation. Far better is an antenna of 50 feet or more outside, which would be connected to ANT2.
  5. Note that this circuit requires a good Earth ground. A suitable location is a metal cold water pipe.
  6. To use the set, place C2 at about midway, set R1 fully counterclockwise and then turn on S1 and allow the tubes several seconds to warm up. Increase R1 until the headphones squeal, then back off. That is when the set is most sensitive. Now tune C2 to the desired frequency. You may have to readjust R1 as you tune different frequencies. With some practice you will figure out how much regen you need as you change stations.
  7. If R1 seems to have no effect, swap the connections to L1.

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Comments

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STEFANO
One Tube Regenerative Radio
Thursday, October 04, 2012 7:04:06 AM
great project. Tested and works perfectly, with excellent sensitivity and selectivity. Thank you. Stefano
Sean O'Connor
One Tube Regenerative Radio
Tuesday, February 14, 2012 10:04:07 AM
Hi, I have put together a short book on regenerative radio receivers: http://www.webstore.com/91359,owner_id,other_items It is mainly about how to build a great regen using bjt transistors but there is some information about using tubes. Many of the new circuit ideas could be adapted for tubes as well.
joe
One Tube Regenerative Radio
Saturday, January 22, 2011 10:36:23 PM
It's been many years since Tandy corporation has put out th one tube radio kit. The voltages required were different although. 1.5 V for A battery and 22.5 for B battery. The internet is amazing!
Ado_PO
One Tube Regenerative Radio
Monday, September 28, 2009 4:11:11 PM
Very simple circuit indeed. Much better selectivity then the OP amp rx. With the described L2C2 resonance circuit It should tune from 0,6 to 3,8MHz but I got only close to 2MHz, when I went higher, I got the squeal which I couldn`t get to disapear no matter where the R1 was set. I used the EF80 instead of the 3A4 as I`m from EU. Anode voltage is not critical as it worked from 20 to 70V. The fillament voltage for this tube is 6,3V so I used a 6V sealed lead accu. I used a old 4kohm military headset for listening. Here is a picture how it all looks like. http://yfrog.com/4a1tuberxj
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