BUILD THE RETRO REGEN RADIO

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eburman
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BUILD THE RETRO REGEN RADIO

Post by eburman » Wed Dec 23, 2015 5:37 pm

I completed this project and it's working great! I've been looking for a good introductory project that would help me learn old school vacuum tube electronics and this was the perfect spring board. I love the warm glow of the tube, The clunky variable air capacitor and learning how to wind my own spider web antenna coil. Building the hardboard chassis was a good learning experience too!

I see that there are quite a few references to this type of single tube, low voltage, regenerative receiver on the web but no one has done a better job in providing a step by step guide from beginning to end. It seems that most of of the broadcast band is bunched up toward the far clockwise end of my air capacitor. Is that normal or did I get something wrong? Maybe it has something with to do with how the spiderweb coil is wound? Perhaps you optimized it for the European broadcast band rather then the U.S.? Otherwise I'm very happy with the performance. I love tweaking the regenerative circuit for maximum sensitivity and selectivity. It definitely requires a good external earth ground connection and for me an external antenna is a must.

It also seems to work a bit better with a lead acid battery. There's less hum then when I use my wall wart power supply. There are a few typos here and there in the article but nothing major and as long as you follow the schematic, pictures and diagrams, then everything should work out. The only other thing that might help is if there were a few pictures showing the layout of the completed radio from above. That way I would have felt more certain that I was connecting things up correctly. I made a few initial wiring mistakes but by checking and double checking my work each step of the way I was able to catch them.

I hope that others consider building this project and post their experiences. It's well worth the time and effort. Thank you so much putting so much into it Dick. I very much appreciate it. Maybe you have other vacuum tube projects in mind? Maybe you have more advice regarding expanding it for SW reception? Have you perfected the Europe on one Tube idea yet?

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VernGraner
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Re: BUILD THE RETRO REGEN RADIO

Post by VernGraner » Thu Dec 24, 2015 3:12 pm

Hi!

Just thought I would let you know that I notified the writer of the Retro Regen Radio article about your question (above). I hope he will jump in here and get an answer for you soon. :)

Vern
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eburman
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Re: BUILD THE RETRO REGEN RADIO

Post by eburman » Fri Dec 25, 2015 10:59 am

Thanks Vern! I mainly want Dick Whipple to know that I enjoyed his well written project. It's unique and diverse articles like this one that ensure that I keep re-upping my subscription to Nuts and Volts Magazine! The best hobby electronics magazine out there.

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Lenp
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Re: BUILD THE RETRO REGEN RADIO

Post by Lenp » Sat Dec 26, 2015 11:38 am

Old trick for dial tracking issues....
If your variable capacitor has outside plates that are slotted you can bend them outward to change the capacitance. This affects the linearity of the tuning and may open up the bandspread some. This worked well on superhets but is worth a try for the regen.
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

dyarker
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Re: BUILD THE RETRO REGEN RADIO

Post by dyarker » Sat Dec 26, 2015 12:49 pm

eburman,

Is the variable air capacitor 2 sections? That is a set of fixed plates with a set moving plates on the shaft, and also a smaller set of fixed plates and smaller moving plates? Those are two separate capacitors on a single shaft so they tune together. The second section is for the oscillator of a hetrodyne receiver. If you accidently parrallel the sections building a regen, the band will be compressed to one end of the rotation as described in first post.

Cheers,
Dale Y

eburman
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Re: BUILD THE RETRO REGEN RADIO

Post by eburman » Sun Dec 27, 2015 10:26 am

Thanks Len and Dale for your ideas and suggestions. I used a single section variable air capacitor which I think is identical to the one suggested by Dick. I think I've connected it up correctly but for some reason the commercial AM band is all bunched up at the far end. The top end of the band may not even be accessible. I think I have two viable options. I could rewind my spider coil to shift the band more toward the middle of the variable capacitor but I'll have to do some research to understand how to appropriately reduce or increase the number of coil turns to achieve that. That's probably what I should do for best performance but it'll means a lot more work. Alternatively I could swap in a variable capacitor with a built in reduction drive to mechanically spread things out a bit more, but that won't help if the top end of the band is cut off. I think I'll try that first. At any rate I'm coming to realize that trial and error is a big part of old school radio electronics. Thanks again for your ideas. I just got a used copy Radio Receiver Projects You Can Build by Homer L. Davidson through Amazon. It's full of more great projects using vacuum tubes and other solid state projects. An so it begins....

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Re: BUILD THE RETRO REGEN RADIO

Post by dyarker » Sun Dec 27, 2015 10:42 am

((I need to read the whole thing before responding))
Dale Y

richwhip
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Re: BUILD THE RETRO REGEN RADIO

Post by richwhip » Tue Dec 29, 2015 3:32 pm

Sorry for the delay in responding. Naturally I am pleased that the article was well received. Thanks for your constuctive comments.

My explanation for restricted band coverage requires a little background. For a variable capacitor to cover a complete frequency range for a given coil inductance, the rf circuit's loading capacitance has to be small in comparison to the minimum of the variable capacitor. In a broadcast band circuit, the inductance of the resonating coil would be chosen such that the 365 mmf variable capacitance fully closed (maximum capacitance) resonates at the low end of the dial or about 550 kHz. Then, with the capacitor fully open (minimum capacitance), a small trimmer capacitor in parallel would be adjusted to resonate the coil at 1650 KHz. Thus, the entire broadcast band is tunable over the range of the variable capacitor. The problem with the Regen Radio circuit is that it presents significant loading capacitance in parallel with the variable capacitor. The result is that much of the variable capacitor's open-end range is negated causing the tuning range of the variable capacitor to be considerably narrowed. There's not much you can do about this. I made a version of the Regen Radio with plug-in coils and a smaller variable capacitor to better cover shortwave bands. One might make a coil for both the upper and lower broadcast band.

eburman
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Re: BUILD THE RETRO REGEN RADIO

Post by eburman » Tue Dec 29, 2015 5:30 pm

Thanks for your reply Dick. Much appreciated! I gather from your reply that everything is working pretty much as might be expected given the limitations of the regenerative receiver? I'm good with that. I was thinking that maybe I didn't wind the antenna coil correctly for optimum performance. But based on your reply I'll just swap in a tuning capacitor with a mechanical mechanism for fine tuning the system. It seems that there are trade offs that have to be made when using a fixed antenna coil. Especially if you want to keep everything simple. Still, I'm loving the overall performance of your project. Thanks again for a really worthwhile introduction to vacuum tube radios!

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Re: BUILD THE RETRO REGEN RADIO

Post by richwhip » Wed Dec 30, 2015 7:31 am

I am traveling at the moment with limited internet connectivity. On still another version of the Regen Radio I used a variable capacitor that sported a gear reduction on the tuning shaft. It was a dual gang capacitor and not appropriate for the article, but it did the trick for easier tuning. You could add a second smaller cap in parallel to the existing one to use for fine tuning. Something on the order of 25 to 50 Mumford would do.

Also, wanted to let you know I am near completion of a Single Ended Triode article hopefully you'll see in Nuts and Volts in the not to distant future. Meanwhile, if I can be of help, don't hesitate to get in touch.

eburman
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Re: BUILD THE RETRO REGEN RADIO

Post by eburman » Tue Jan 05, 2016 7:18 pm

Hello Rich (or do you prefer Dick?): I hope that you are enjoying your travels. Thanks so much for your prior reply. So, as I mentioned, things are working sort of well except that the entire AM broadcast band is bunched up at the extreme end of the air variable capacitor tuning range (far clockwise, lowest capacitance). When I connect my external long wire antenna with earth ground it gets even worse. You suggested adding a 25-50 "Mumford" capacitor in parallel? I'm not sure what a "Mumford" is. Maybe microfarad? But that doesn't seem right to me. I did try adding various pF range disc capacitors (10-68 pF range) in parallel but that didn't help. They just shifted things even further to the extreme right end of the air variable range. It seems to me that I need to decrease the capacitance of the variable capacitor. So I experimented with adding various capacitors in series with with the variable capacitor. That helped quiet a bit. I experimented with 10-470 pF capacitor values. A 68 pF capacitor seemed to provide optimal performance. The band spread was much better but I still topped out at 1.4 MHz no matter what I tried. Given that the AM band extends from .535 to 1.705 Mhz I'm missing quite a lot of the top end of the band. So, maybe the problem is with the antenna spider coil after all???? I've been avoiding that consideration because it took a ton of effort to wind that coil. But, maybe I did it wrong??? Should I try again? Is there maybe a more optimal ratio of turns that I should be trying? Any ideas you have would be much appreciated.

eburman
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Re: BUILD THE RETRO REGEN RADIO

Post by eburman » Tue Jan 05, 2016 8:04 pm

Ahh, now I get it!.... mmF = mumford = pF. Beginning to pick up the old school vernacular! Also, I re-read your initial reply. So I think you are saying that the band range is necessarily going to be limited by the constraints of the circuit design. If that's the case, I'll just add in the 68 "mumford" capacitor in series with the variable cap which seems to help spread the band out and maybe I'll swap in a variable capacitor with 6:1 mechanical turn ratio. I'll still be limited to about a 800 to 1400 KHz tuning range but I'll just have to be satisfied with that. The project still is a winner even with those limitations! But once again if you have any other suggestions that don't require major modifications please let me know. Cheers!

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CeaSaR
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Re: BUILD THE RETRO REGEN RADIO

Post by CeaSaR » Wed Jan 06, 2016 3:54 am

The design is a classic L-C tuned receiver. In order for it to be able to do its job correctly, you must tune both parts of the tank. You've sorted out the C section, but now you must adjust the L section. On commercial sets, they would use a slug loaded coil and would go through the prescribed setup using test equipment. Without that equipment, you have to empirically adjust your coil to get the tank circuit to work within the desired range. For air core coils, this is done by:

Spreading or tightening the coil (for simple one layer coils)

Removing or adding windings (for complex multilayer coils)

Switching or adding taps (for tapped coil designs)

All of these raise or lower the inductance of the coil. In your case, you need to slightly LOWER your coil's inductance to RAISE the tank circuit's center frequency. I can't find my copy of that article to see what the coil should be, but either very slightly spread the coil or remove a half-turn of the winding at a time and check. This should get your full tuning range.

CeaSaR
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VernGraner
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Re: BUILD THE RETRO REGEN RADIO

Post by VernGraner » Wed Jan 06, 2016 10:12 am

CeaSaR wrote: I can't find my copy of that article to see what the coil should be...
Does this help?

http://nutsvolts.texterity.com/nutsvolt ... pg=26#pg26

:)

Vern
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CeaSaR
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Re: BUILD THE RETRO REGEN RADIO

Post by CeaSaR » Wed Jan 06, 2016 12:55 pm

Sure does, Vern! Thanks!

So, the coil you need to adjust is L2, the vertical coil, not the spiderweb. Start by undoing 1/2 to 1 turn from the bottom and then check the tuning. If it improves, which it should, keep going in similar increments until you have it working to your satisfaction.

Take note, you may need to readjust the capacitor section when you get the coil sorted out.

Happy listening!

CeaSaR
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