This version removes the direct coupling of Q2 in the previous version and increases the emitter resistor as well, finally the regeneration control is moved to the emitter circuit. The result is little better performance with less loading of the tank and less detuning caused by regeneration adjustment. Probably other optimizations possible also. I tried to make this thing not work…and it was difficult requiring extreme deviation from shown component values. It should be very easy to get this thing up and running with all sorts of tank circuits. It works well with a broad range of supply voltages also the values for R7, R8, R9, and R10 have a wide range of functional values. So one probably wants to start with my values and then tweak for best performance, once the circuit is up and running.
Schematic Diagram(modified TDA7052at circuit 07/01/2015)
Circuit Salad 
Thanks for posting this. This is a circuit topology that I’ve been wanting to try for a while (differential pair with Q1 high-Z collector heavily coupled into tank, and Q2 low-Z base lightly coupled into tank).
It might be fun to try a “floating diode” detector at the tank (e.g. see Charles Kitchin’s “A Simple Regen Radio for Beginners” at http://www.arrl.org/files/file/Technology/tis/info/pdf/0009061.pdf) instead of your Darlington pair detector. The floating diode detector might allow your circuit to run off of a single 1.2V cell; I think the differential pair oscillator should work fine at 1.2V but your Darlington pair detector requires more voltage, where as the floating diode should work fine even at low voltages. However, then you have the problem that the floating diode detector apparently needs a high-Z AF load for good detector efficiency.
your diode suggestion gave me an idea I am going to try, but I will say the darlington has gain and decent fidelity so its at least worth experimenting around with.
Check out my new version I just posted…its tailored for the low voltage operation you are describing and works very well
hi Ray,
thank you for the great site with lots of ideas and information!
i’d like to build this one, because i don’t have jfets, too bad. i also don’t have the TDA7052, but have a few LM386’s. so i tried to LTspice simulate that, and have a whole lot of newbie questions just regarding simulating a regen radio with LTspice.
if you have the time to help with that, that’d be great. if you don’t, and could point me to somewhere for answers, that’d be great too, thank you!
i don’t know how to include LTspice files and/or pictures here, so…
i used SFFM(0 10mV {fc} 0.5 {fs}) as the input voltage setting, an attempt of giving it a modulated signal, {fc} is Frequency Carrier, {fs} is Frequency Signal, and fc=98mhz, fs=1khz. the modulation index was set to 0.5, for i don’t know what is a good number to use here. is this the correct way of doing it?
after simulation finished running, and when i clicked on the hot side of this signal voltage source, i got a
1khz sine wave, and that is supposed to be the original signal, i didn’t get any modulation of it, let alone by a carrier of 98mhz. why is that, who did i do wrong?
at the LM386 output, i got a 1khz sine wave of about 17mV, where as the signal amplitude is 10mV. why is it so? is it supposed to be so, or i did something wrong?
last question this round, would the output of the LM386 be enough to drive a small speaker?
thank you Ray for your time!
armVeryStrong
LM386 will work fine may need to pay attention to decoupling. I normally don’t try to simulate regens as complete receivers. The regen is really just an oscillator so I have simulated my circuits as oscillators using device models such as the 2n3904..etc. The idea is to build an oscillator that can be made to build to oscillation slowly and and also at a very low level of amplitude.
not sure what you are trying to test with your simulation below:
i used SFFM(0 10mV {fc} 0.5 {fs}) as the input voltage setting, an attempt of giving it a modulated signal, {fc} is Frequency Carrier, {fs} is Frequency Signal, and fc=98mhz, fs=1khz. the modulation index was set to 0.5, for i don’t know what is a good number to use here. is this the correct way of doing it?
after simulation finished running, and when i clicked on the hot side of this signal voltage source, i got a
1khz sine wave, and that is supposed to be the original signal, i didn’t get any modulation of it, let alone by a carrier of 98mhz. why is that, who did i do wrong?
Also 98 MHz will not work with this circuit..beyond say 20 MHz it will become too unstable. My advice is to just try building one and have fun.
i don’t have any 2n2222 Ray, will need to use others if build now.
so does the Transition Frequency (fT) of a bjt have to match the frequency to be tuned to? how much higher than the carrier frequency does it need to be, in order to have oscillation?
or more generally about oscillators, there is a relation between the bjt fT and the oscillating frequency, ie., the oscillator will not oscillate at a requency higher than its fT, correct?
armVeryStrong
(must say Armstrong was a genius.)
hi Ray,
would you care to comment on what the positive feedback loop is for the oscillator?
is it L1->R10->Q1? or C9? or both?
thanks a lot!
AVS
Q1 forms a common base amplifier with the tank in the collector circuit Q1. Q2 forms an emitter follower, which samples the output of Q1 and then couples positive feedback through C9 back into the input of Q1. If you redraw the circuit you can also interpret the circuit as a variant of a cross coupled oscillator.
I built this receiver today. Works very well. In fact, it works better, at least for me, than the very low voltage junkbox regen that you described in another post.
Thanks for all of the great circuits you share on this site!
Yes I am happy to hear that it works for you. Regens are fun to build. Hopefully some of my ideas will spur other designers/experimenters to come up with something even better.