While working on my Kraft RC radio conversion I had to wind some coils out of magnet wire. My mind suddenly drifts back to when I was 11 years old. I took my birthday money and went with my father to a TV parts store. My dad had a part time TV repair store with my uncle. The parts guy there knew my father and he looked at the page of the project I wanted to build. It was a one transistor regenerative radio that would pick up CB radio and 10 meter Ham radio. The man there looked at the parts list and he started bringing the parts one by one back to the counter and he even threw in a FREE earphone!
I took the parts home and mounted them on a piece of leftover kitchen paneling. I used brass nails for the circuit points. I used contact cement to hold the ARCO caps to the board. I tuned it on and Nothing! I went over that circuit until the cows came home! A few weeks went by and my dad bought me a Walkie-Talkie. Then on Christmas we built a Regen Radio Kit together.
Over the years I have thought about that circuit. It was the only circuit that I could not get working. I came to the conclusion that the FREE earphone I got was the wrong impedence. So there I am am winding the coils for the Kraft transmiter the same way I wound the coil for that project 50 years ago. Over the years I have searched for that old circuit. I went on a Yahoo group and told my story. One guy told me all the old electronic magazines were now indexed and free as a PDF. I went looking through the Popular Electronics issues around 1960 when my dad had the TV repair shop. I remember the circuit used a peaking coil. So I put in "Regen, Peaking Coil". Bingo! There it was! The first thing I looked at was the earphone. Yup! It called for a high impedence earphone not a 8 ohm freebe! So I built the circuit just like I did 50 years ago. I found the ARCO tuning caps in one of my parts bins. I used GOOP this time to mount parts and plain nails for tie points. I had an old Germanium transistor and socket. I used a phone earpiece and a transformer to make a high impedence earphone. The parts got mounted on a piece of grey PVC. The 9 volt battery was connected and I had HISS! I turned on my retro Kraft at the other end of the house. I picked that up! Then some CBers coming by my house on the highway. That was that!
50 Years Later!
50 years later the circuit was working!
The Madness Continues!
The Madness keeps right on going! I went looking for another Regen to build 50 years after me and my dad built one I got for Christmas. I found a simple circuit By Charles Kitchin on the web. It uses a 2N2222A in the oscillator. It does work but it has some annoying problems. The Regen control is a bear to adjust. Hand capacitance is also a problem. I added a two turn winding to the antenna coil. One end goes to ground and the other end to your antenna. This made the radio better.
A two turn winding added to coil.
You might notice I use Perf Board and Flea Clips. I proto a circuit using a solderless protoboard. I then draw it up in Windows Paint using my Perf Board drawing system. Here is a drawing you can put in Windows Paint!
Regen Perf Board Drawing
Board ready for Debug
The circuit board in the picture is for a Kitchin FET unit. During the debugging I check to see the audio section is working first. Use headphones!! I touch the top of the volume control with my finger. There should be a hum. I then make sure the volume control is working. I then measure the voltage at the oscillator section across the zener or the three diodes in series. On my newest FET unit I left off a ground wire. I found it during the Debugging. I don't expect the circuit to work great at this point. But I do want to have controlled volume and Regeneration. Getting stations with squealing noise is music to my ears. The circuit will calm down once the parts are mounted. No noise is bad news!!!
Kitchin FET Regen
You may notice I mention Charles Kitchin in my page. I do that because others don't! They take his name off his diagram and insert their own! Then you got the redrawers! It took me days to get a handle on these circuits. I proto boarded and wired several circuits. Kitchin's FET unit is the best! the Bipolar circuits do work but the Regen control is scratchy and tough to adjust compaired to the FET unit using a tuning cap for the regen control. My only changes to the Kitchin FET are as follows. I reversed pins 2 and 3 on the LM386 to prevent oscillation. I added a anti hiss circuit to the LM386 as found in the Guitar circuits using a LM386.
Kitchin FET Regen
As you can see I built a second Kitchin FET Regen. This time I added a Vernier Dial. I had a problem with the unit. The 100pf Throttle cap was stiff! I turned it around a few times. Suddenly my circuit went haywire. So I swapped the main board with my other unit. It was OK. I was tired and missed the obvious. During shipping the 100pf cap got a bent plate. I did not see it at first. Using an ohm meter I could see the plates only touched when the cap was in the area I needed. I was able to straighten out the plate.
Kitchin FET Regen
I did learn something new working on this project! Most of the FET Regen circuits use a 160pf for the main tuning capacitor. If you use a 365pf cap the stations will be all bunched up and the circuit will stop working when your cap gets to about 250pf. What to do? I did some reading! I found you can added a 470pf fixed cap in series with your 365pf. Now all your stations will be spread out over the 180 degree travel. I posted my findings on a Yahoo group. One worried about linearity while a second said he would have to check the finding with his data! Tools!
You can also put a cap in series with your Throttle cap to give you better control. I put a 10pf in series with my 30pf fine tune. A 2pf would be better. Take a close look at Kitchin's and other people's radios. You will see they added these caps. My Throttle cap is a 100pf that reads 120pf. I got a 100pf in series with it. There are online calculators you can use. If you put a 2pf cap in series with a 50pf tunable cap it will become a 2pf tunable. A Nitpicker will give you the real value. If you put a small cap in series with a big one the value will less than the smallest cap. Sweet! Now you can use the variable caps you already own!!!
Email: John a quick question
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