This is the first project that I worked after long time absent playing electronics.
I remember when I was at Junior High School, at that time the source of learning electronics was quite limited here, no internet, just some excerpt article clipping or photo copy from borrowed electronic magazine. But things has been changed, I gathered and understand so much information from various electronics web site. See Ian Purdi – electronics tutorials web site, I am start learning from here, understand such thing named coil or inductor, this coil related thing probably nightmare among us, for example given a schematic, the coil specification was : J. W. Miller 112-H6, or toroid T50-6…. ?? What is this thing ? Where to buy it ? Can I make it ? No one sell it here, I ask a service man, maybe he know something from his experiences, he also did not have an idea and could not give answer that I needed. So mostly the schematic journey was ended here.
My enthusiast passion was at radio frequency project such as walkie talkie, SW radio etc.. Some friend have so much progress than me, but he was into hi-fi amplifier things that I am not interested.
I just feel that radio ( receiver ) thing is amazing, a magic thing !
Back to Ian Purdi’s tutorial, there are lessons about oscillator, he teach how to calculate and constructs such coil, calculate the working frequency etc. These are the lessons that I want so long !
He also have a nice project to build : Regenerative Radio a la Kitchin. Wow , now reading this schematic is very enjoyment, I could understand even could design my coil for desired working frequency, I recommended this project for: easy to build ( relative ), not so much components, clear explanations and instructions, cheap and the result could be very nice. You will have enthusiasm and confidence to the next projects. And at last getting new experience with art of unusual tuning.
Components are not critical, any available FET can be used, just give attention to coil construction :
1. Note how to wind, L1, L2 & L3 all must be in same direction. Case of error found in a friend, one coil in in other direction.
2. Another case at L3, coil winding is not enough, for example it mentioned 3 reels, but only 2.5 reels coiled, so the regeneration does not occur or too weak, if necessary make experiment by first adding 1 to 2 reels at L3, and see how is the result.
3. Space between L1, L2 and L3 according to some article are spaced about 3 mm, but according to my own experiments, space is closed.
4. L3 position is lowest, space between L3 to ground plane pcb not to closed, try at least 2 cm.
This is the first time I try assembling methods so called “Manhattan Island”, where a small piece of pcb glued with super glue to mother board ground plane pcb. Nowadays I preferred “Rat Nest” or “Ugly Construction” assembling method, this is much faster but at some point still use Manhattan Island as a pad, but I do not use super glue any more, I used a double ( adhesive ) tape, very quick. This kind of tape have a black sponge with green insulation, I see glazier used to attach the mirror to the plywood, with time, it become stick very strong. If exposed to soldering heat, let it sit until cool, he will stick again. Scissors the double-sided tape into small pieces, according to the size of the pcb pad that will be attached.
– Adding FINE REGEN using diode or LED as a varactor, in my opinion is absolute to be added, this addition make regen setting much smoother, much easier.
– Capacitor C3c with value 5 pF is good enough for fine tuning in AM mode, but for SSB mode this is somewhat oversized, replace with 1~2 pF.
– Potensiometer for a long time tend to become dirty and make a noise ” crack – crack” could be replaced the VOLUME potensiometer with fixed resistor with SELECTOR SWITCH , while for ATTENUATOR potensiometer could be replaced by plastic varco, see schematic of AA5TB.
– One thing that has not been satisfying me, is the sound output of the LM386 is too small, I try to add a preamp, the results are not in line with expectations, resulting in the motor boating, and sound output also not increased significantly, please advise from readers. The AF amplifier experiment ended with TBA810, still too weak.
Fortunately I have built my guitar amplifier using LM 1875 ( see my amplifier at http://amplifier-guitar.blogspot.com/), plus a FET preamp. I can use this with my regen, sound is so powerfull, remembering me to the voice of my grandpa’s Philips old valve radio.
Recently I read an article at QRP-SWL Homebuilder web site ( this is one of the very good site ) about LM1875 and e-mail to owner site Todd VE7BPO. I asked him a suggestion for a preamp that suit for this configuration ( homebrew rx + pre-amp + LM1875 ). A homebrew rx could be : kitchin regen, PA2OHH shortwave rx, PY20HH DSB TRX etc.
Not too long, he replied my letter explain that he make and tweak a pre-amp for me ( thanks ! ) :
I liked your blog.
Based on some work by Douglas Self; a prodigious Audiophile EE/author — This is the best “popcorn” AF pre-amp I’ve built — in that with a load R of ~1K or greater the output stays clean until above 7.04v peak-peak with only ~ 5 mA of current . Low distortion at .002%. The boot-strapping boosts Q1 gain and the current source on the emitter follower extends the ability of this amp to drive even smaller load impedances quite well.
This should boost up your signal nicely. The 1K input resistor called “R” can be increased or decreased. The minimum would be 100 ohms as to prevent oscillations. If your input signal is too large and gets distorted, increase R to between 1K5 to 4K7.
The output 1K resistor can be your volume control pot or any load greater than ~ 1K
I know it looks a little “busy” but this amp is staple, very clean and can swing a large AC signal
MINI REGEN a la ONNO (PA2OHH)
This is another regenerative radio from Onno ( PA2OHH ).
The results were not too good, noissy compared with Kitchin regen. There is interference from FM broadcasts, but this can be overcome by adding a 10 pF capacitor in transistor T1. But I like it smal size.