1933 Regen Project


Monday was spent finishing the coil winding for my present bench project, a 3-tube regenerative receiver. The receiver first appeared in the January '33 QST article, "Rationalizing The Autodyne", by George Grammer. I tried to stay true to the original design, both physically and electrically, as much as possible. Where period components were not available, they were manufactured. Several capacitor are 're-stuffed' cases and some resistors have been physically altered to resemble era-appropriate styles. The one deviation I made from the original circuit was to remove the B+ (200VDC) from the headphones by going to impedance-coupled audio, which blocks DC from the headphone circuit. After finishing the coils and doing a quick re-check of the wiring, I held my breath and applied the power.






Much to my surprise and delight, the receiver worked immediately. It took me some time to find the correct control settings and combinations that seemed best but eventually its operation became familiar. Here are a couple of short recordings, crudely made via connecting the computer across the high-impedance headphones, as I tuned across a somewhat noisy 40m band in the evening.







Now although the receiver appears to be working, I'm not 100% convinced that it is working as well as it should. It's difficult to know exactly how it should perform when at its best as it really can't be compared to any of our modern-day receiving systems. Just what did 'good performance' sound like in 1933?

I have some reservations about one of my tubes. It's a '78' from my junk-box stash and has a large red '?' inked across the glass envelope. I may order some NOS '78's or even some more modern '6D6's, to see how they perform. On the plus side, the oscillator seems very stable and there is absolutely no 'hand-effect' on tuning, a common problem with many regens. Peaking up the RF stage tuning causes no pulling of the oscillator but the '78', although a hot-performer in 1933, provides plenty of tube noise as well, if the gain is set too high. I think the main advantage of having the tuned RF stage is to add RF selectivity and eliminate any bleed-through from some of the blowtorch shortwave signals just up the band. Tuning seems best when its gain is set between fifty and seventy-five percent of maximum. The large drum dial, in combination with the small bandspread capacitor, spreads 40m across most of the dial and makes for easy tuning although there is a small amount of backlash.

Another thing I noticed is that it seems to be very receptive to spurious computer birdies, with the laptop sitting just a foot away. Perhaps its unshielded top and bottom are the cause of this as I don't hear any of the signals on my main station receiver.

Comparing it to the two-tube regen in my Paraset, the Paraset sounds much quieter and generally sounds more sensitive ... but it uses more modern tubes, '6SK7's, first introduced in 1938, five years after the '78'. The selectivity seems as good, if not better, than the Paraset, which I consider an excellent performer. The Paraset also sounds just as good as my National SW-3, which was produced in the early 30's ... so the new regen is likely not as quiet nor as sensitive as the SW-3, probably the best simple regen of its day.

Perhaps some newer tubes will make a difference in performance and maybe my expectations are too high. In any event,  the closing paragraph of Grammer's article may be more telling that I originally thought:

"The set as it stands is not perfect, of course; nothing ever is."

Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

8 Responses to “1933 Regen Project”

  • BOB LECH AF2Q:

    Steve,
    Sounds OK to me and I bet you had fun building it.
    Really sounds good for a regen and if your going to tweak it up,and use a better speaker its going to sound great.
    Nice work.
    Thanks for sharing
    BOB LECH AF2Q

  • Bob W8RMV:

    You’re sick Steve. Regen? Old tubes?? LOL. I too, share this same illness. I don’t know what it is about Regen’s but they just appeal to me even tho they can be a PITA compared to modern rigs. Thanx for sharing. Looking forward to the update.- Bob

  • Jeff K9JP:

    Outstanding Steve,

    I think your ReGen receiver sounds just perfect! This winter the band will sound wonderful and the summer clicks and noise will be long gone. I recently have been restoring life to 1940’s table top AM radios and enjoy everyone. My be a ReGen is some thing for me to try this winter.I do wish, I had your skills and talents! Keep having fun and enjoy the hobby.

    72/73 de Jeff K9JP

  • peter kg5wy:

    Brings back the memories.
    🙂

  • Rick N3QOU:

    Very Interesting read! I too love the older equipment!
    like Jeff K9JP said it does sound great! Keep them coming.
    Thank for sharing!
    73’s Rick
    N3QOU

  • Joe Cro N3IBX:

    Hello Steve, I really like your “Rationalized Autodyne” and think you did a superb job building it after the original article. I have an original built sometime after the article was published. It came with a complete set of Hammarlund built coils for it. Hammarlund actually marketed a coil set for the autodyne so I can concur that it must have been a popular set in the mid 1930’s.
    I really like your comments abiut it’s performance. My set isn’t as good as my National SW-3 either and find the SW-3 a superior performer. Regardless, you built a piece of Amateur Radio history and did a great job of it at that. I hope you get a loit of enjoyment out of it. If I can help you in any way with my original one or with coil winding data please drop me a email.
    Very best regards,
    Joe Cro N3IBX

  • Steve VE7SL:

    Thank you for all of your encouraging comments! It was a fun project but it must have been a challenge for builders in the 30’s as their soldering equipment was very crude compared to what we work with today … there were some very tight quarters at times so it must have been difficult.
    Joe … I had no idea that it was as popular as having Hammarlund market coils for it. I guess being published in several of the Handbooks would give it lots of exposure. It’s good to hear that your comparison with the SW-3 mirrors my own experience. I would love to see some pictures of your original autodyne if that is a possibility?
    I played with the receiver some more last night and am getting more familiar with optimum control settings. As well, conditions were much better than my first night of testing. I am now more confident that it is working fairly well after all, as it was very easy to hear several east coast signals as well as several Europeans last night on 40m CW. It is close to the same sensitivity as the SW-3 but I would still give the nod to the National which is an extremely well executed design. Last night, the band was just full of signals and tuning was very easy once the proper levels of RF gain and regen were set. One nice feature with this radio is that the regeneration, once set, does not need to be constantly tweaked, as it does in many other designs … it also goes in and out of regeneration smoothly. I think its a keeper and will probably not need re-tubing after all.

  • Doug KM6OR:

    Hi Steve. Nice job on that “Rationalized”! I wonder what you have found out its performance comparisons in these years since it was first built? I have built a SW-3 type circuit in the past as well as a Gainer with #78 or #77 RF stage. I found these tubes excellent. Actually, the #77 makes a great Detector and RF amp. How is it working now? Where did you ever find that tuning dial/drum? Any chat or info will be greatly appreciated. 73’s, Doug, KM6OR ex WB6LXA.

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