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RE: [regenrx] more 3A5 twinplex experiments

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  • Larry Beaty
    Just a little thought out of the box here. What if: you simulated a 3:1 transformer with a solid state circuit just to see if it would work. I can understand
    Message 1 of 13 , Apr 7 6:12 AM
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      Just a little thought out of the box here. What if: you simulated a 3:1
      transformer with a solid state circuit just to see if it would work. I can
      understand cost! I think Mouser has some reasonably priced interstage
      transformers, but golly out where you live, shipping would be expensive!



      Larry



      From: regenrx@yahoogroups.com [mailto:regenrx@yahoogroups.com] On Behalf Of
      kyoritsu
      Sent: Monday, April 07, 2008 5:40 AM
      To: regenrx@yahoogroups.com
      Subject: [regenrx] more 3A5 twinplex experiments



      More results from experiments with the 3A5 double triode twinplex. And sorry
      for the
      length of this post.

      In my continuing attempts to get more audio gain, I tried keeping the regen
      detector stage
      at 36V, and raised the AF stage in 9V steps up to 135V. (Yes, I'm using 9V
      batteries for the
      B+). Surprisingly little difference and not worth it. In addition, the
      current did increase
      from a little under 1mA to about 7mA, so from the point of view of battery
      life, higher
      voltage can't be recommended.

      I then tried keeping the AF stage at 36V, and raised the detector stage in
      9V steps, from
      27V up to 117V. The results were interesting. Of course, it natrually shifts
      the point of
      regeneration. However, it also changes the nature of the point of
      regeneration. At 27V, the
      regeneration point is sort of weak and vague, you have to listen for it,
      tune off center
      frequency to hear the audio beat. As the voltage is raised, this point
      becomes sharper, a
      clear '...tssss', no mistaking it's in oscillation. At the highest voltages,
      it's rather ugly and
      aggressive. I like it around the 36V to 54V range. I thought even though the
      set has a
      throttle capacitor for regeneration control, having a voltage divider pot
      for the plate
      voltage might be a good addition. At least, to experiment with, try
      different settings,
      perhaps find the sweet spot for different frequencies, a combination of a
      certain throttle
      setting and plate voltage.

      The good thing about 27V on the detector stage: very low current, about
      500uA. Goes up
      to about 4mA with the highest voltage.

      Something else about raising the voltage on the detector: it made the weak
      signals, just
      barely intelligible, noticeably louder and easy to understand. Almost good
      enough to fix
      the low audio problem. The 3A5 is a power triode, low mu, not much voltage
      amplification, plus it needs a fairly strong signal to drive it. With strong
      stations, there's
      plenty of signal, far too much, the set should have a volume control. But
      the weak signals
      sort of just drop off into the noise. With higher voltage on the detector,
      the grid leak audio
      amplification increases, providing a stronger driving signal for the power
      stage amplifier.
      Gets it over the hump. At least, that's the way I understand it.

      I haven't tried a 1:3 step-up interstage transformer yet. Want to, but I
      don't have one, and
      I'm reluctant to buy one (not cheap). The original idea was to build a type
      19 Twinplex
      using the 3A5 tube, using the same very simple design and a minimum of
      parts, to see
      just how well it could perform. I suspect the stereo phones I'm using just
      require too much
      power. I tried adding an op amp stage, and it works great, plenty of audio,
      solves the
      'problem'. But the point was stay within 1930s technology as well as keep it
      simple and
      inexpensive.

      One more observation about the detector stage: it will not oscillate with
      more than a foot
      or so of wire attached to the tank circuit. Ten feet or so will work if put
      through a 2pF
      capacitor, but not longer. The best way to couple the signal from the
      antenna is a single
      loop of wire around the coil, about 1/2 inch away, and the end free, not to
      common. Then,
      with the op amp added, it seems to be as sensitive as my R1000 yet somehow
      sounds
      'better', better fidelity, less noise.

      Thanks again for all the advice and suggestions. I may be reinventing the
      wheel but it's
      been fun.

      Rob





      [Non-text portions of this message have been removed]
    • Bill M
      ... Mouser has the little transistor xfmrs which can be reasonably effective. p/n 42TU002-RC for example is a 5:1. There s a noticeable loss of audio
      Message 2 of 13 , Apr 7 7:07 AM
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        Larry Beaty wrote:
        >
        > understand cost! I think Mouser has some reasonably priced interstage
        > transformers, but golly out where you live, shipping would be expensive!

        Mouser has the little 'transistor' xfmrs which can be reasonably
        effective. p/n 42TU002-RC for example is a 5:1. There's a noticeable
        loss of audio compared to a real man-sized xfmr so that might not be the
        ideal answer if maximizing volume is the goal. I use often these as
        replacements in old 1920s tube radios.

        The other off-the-shelf option are the Hammond ones from AES or
        Radiodaze but they are about $14/pop. Very good xfmrs and wouldn't be a
        problem to ship.

        The Hammonds are sometimes better fidelity wise than old original 1920s
        xfmrs which can be had at PTOP in the $10-15 range. I just bought about
        a dozen for my projects. Ya gotta love Flat-rate Priority Mail even
        for foreign destinations :)

        www.oldradioparts.com

        GL,
        Bill
      • Bill M
        ... Over the past few days I ve been doing almost the exact same tests as you have, posted at http://theradioboard.com/rb/viewtopic.php?t=937 I m using a pair
        Message 3 of 13 , Apr 7 7:15 AM
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          kyoritsu wrote:

          > I haven't tried a 1:3 step-up interstage transformer yet. Want to, but I don't have one, and
          > I'm reluctant to buy one (not cheap). The original idea was to build a type 19 Twinplex
          > using the 3A5 tube, using the same very simple design and a minimum of parts, to see
          > just how well it could perform. I suspect the stereo phones I'm using just require too much
          > power. I tried adding an op amp stage, and it works great, plenty of audio, solves the
          > 'problem'. But the point was stay within 1930s technology as well as keep it simple and
          > inexpensive.

          Over the past few days I've been doing almost the exact same tests as
          you have, posted at http://theradioboard.com/rb/viewtopic.php?t=937

          I'm using a pair of 5676 and my biggest problem seemed to be a very
          narrow voltage window getting the 5676 to regenerate controllably
          without going into oscillation. I think I have cured that. My biggest
          problem in getting adequate audio turned out to be my phones. I had
          grabbed a cheapo set of Cannonballs off the rack and was fighting to
          hear anything :) Once I put the good phones (R-14s) on the set it was
          like adding a couple of stages of amplification!

          How are you matching your stereo fones to the ckt? That might be worth
          revisiting.

          Adios,
          Bill
        • kyoritsu
          Hi Hue, thanks for the encouragement. There is probably more to be discovered (as well as re-discovered) about regens. I look at this simple 3A5 receiver and
          Message 4 of 13 , Apr 7 11:22 PM
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            Hi Hue, thanks for the encouragement. There is probably more to be discovered (as well as
            re-discovered) about regens. I look at this simple 3A5 receiver and am amazed by what it
            does. If I still had my license (and a tx), I'd be using it for 40 meter CW.
            >
            > So to maybe summarize your result, higher plate voltage = more
            > usable sensitivity, but more difficult to handle, to control the
            > regeneration?

            Yes, that's it. If I add extra AF amplification, the lower voltage on the detector is no
            problem. I suppose you have to choose between optimizing the RF part of the detector
            stage and the AF part.

            > I don't think you're stuck to a 1:3 audio transformer. I'm sure a
            > somewhat higher ratio would be fine. You're in Tokyo, right, and
            > maybe don't have too many scrounging venues available?
            >
            Japan is not a good country for scrounging. Otoh, you can find almost anything you want
            in Akihabara in Tokyo (if you're willing to pay). Would you believe some tubes from the
            1930s can sell for thousands of dollars?

            > How about the output transformer, what are you using and where
            > did you get that? I expected that raising the B+ over a 3:1 ratio
            > would have gotten you more additional audio than that.
            >
            The output transformer has taps at 5k, 7.7k (I think), and 10k for the primary, 8 ohms for
            the secondary. I'm using it at 10k. Tried the other primary taps, but it didn't help.


            > "Maybe", if i find one, i could mail it to you?
            > What are the size constraints?

            Thanks, but shipping to Japan is just too expensive. I know where I can get one here,
            looks sort of NOS, should be OK. Again, I'm trying to approach this like someone would
            have during the Great Depression, determined to get the most performance from the least
            investment in parts. However, at this point, I've got to find out how well a step-up
            transformer would do, even if I don't end up using it.

            Rob
          • kyoritsu
            Larry, I am a primitive when it comes to circuit design. I believe in tubes, don t trust solid state. However, I may try an interstage transformer meant for a
            Message 5 of 13 , Apr 7 11:34 PM
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              Larry, I am a primitive when it comes to circuit design. I believe in tubes, don't trust solid
              state. However, I may try an interstage transformer meant for a transistor amp. With low
              voltage and current on the 3A5 detector, it might work.


              --- In regenrx@yahoogroups.com, "Larry Beaty" <hlbeaty@...> wrote:
              >
              > Just a little thought out of the box here. What if: you simulated a 3:1
              > transformer with a solid state circuit just to see if it would work. I can
              > understand cost! I think Mouser has some reasonably priced interstage
              > transformers, but golly out where you live, shipping would be expensive!
              >
              >
            • kyoritsu
              Hi Bill, I thought of ordering from Antique Radio, prices are all right, but the shipping is a killer. I m going to keep my eyes open here for a suitable
              Message 6 of 13 , Apr 7 11:43 PM
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                Hi Bill, I thought of ordering from Antique Radio, prices are all right, but the shipping is a
                killer. I'm going to keep my eyes open here for a suitable transistor amp transformer. It's
                good to know they should work.

                Rob



                --- In regenrx@yahoogroups.com, Bill M <radioexray@...> wrote:
                >
                > Larry Beaty wrote:
                > >
                > > understand cost! I think Mouser has some reasonably priced interstage
                > > transformers, but golly out where you live, shipping would be expensive!
                >
                > Mouser has the little 'transistor' xfmrs which can be reasonably
                > effective. p/n 42TU002-RC for example is a 5:1. There's a noticeable
                > loss of audio compared to a real man-sized xfmr so that might not be the
                > ideal answer if maximizing volume is the goal. I use often these as
                > replacements in old 1920s tube radios.
                >
                > The other off-the-shelf option are the Hammond ones from AES or
                > Radiodaze but they are about $14/pop. Very good xfmrs and wouldn't be a
                > problem to ship.
                >
                > The Hammonds are sometimes better fidelity wise than old original 1920s
                > xfmrs which can be had at PTOP in the $10-15 range. I just bought about
                > a dozen for my projects. Ya gotta love Flat-rate Priority Mail even
                > for foreign destinations :)
                >
                > www.oldradioparts.com
                >
                > GL,
                > Bill
                >
              • kyoritsu
                Hi Bill M, I too have been thinking it s the stereo phones I m using. Pardon my ignorance, but what are R-14 phones? Old style cans? What s the impedance? Mine
                Message 7 of 13 , Apr 7 11:55 PM
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                  Hi Bill M, I too have been thinking it's the stereo phones I'm using. Pardon my ignorance,
                  but what are R-14 phones? Old style cans? What's the impedance? Mine are standard 16
                  ohm stereo phones, connected to a 10k to 8 ohm output transformer.

                  I notice my breadboard layout is sort of a drunken version of yours.

                  Rob


                  > Over the past few days I've been doing almost the exact same tests as
                  > you have, posted at http://theradioboard.com/rb/viewtopic.php?t=937
                  >
                  > I'm using a pair of 5676 and my biggest problem seemed to be a very
                  > narrow voltage window getting the 5676 to regenerate controllably
                  > without going into oscillation. I think I have cured that. My biggest
                  > problem in getting adequate audio turned out to be my phones. I had
                  > grabbed a cheapo set of Cannonballs off the rack and was fighting to
                  > hear anything :) Once I put the good phones (R-14s) on the set it was
                  > like adding a couple of stages of amplification!
                  >
                  > How are you matching your stereo fones to the ckt? That might be worth
                  > revisiting.
                  >
                  > Adios,
                  > Bill
                  >
                • Bill M
                  ... Yep, they are old-timers. Here s an example. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160226982541 I believe the R-14s are 2k ohms. There s a
                  Message 8 of 13 , Apr 8 4:37 AM
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                    kyoritsu wrote:
                    > Hi Bill M, I too have been thinking it's the stereo phones I'm using.
                    > Pardon my ignorance, but what are R-14 phones? Old style cans? What's
                    > the impedance? Mine are standard 16 ohm stereo phones, connected to a
                    > 10k to 8 ohm output transformer.

                    Yep, they are old-timers. Here's an example.
                    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160226982541

                    I believe the R-14s are 2k ohms. There's a later version with a
                    different nomenclature that looks the same but they are 600 ohms.

                    Good sensitivity, the audio actually sounds pretty good and maybe most
                    importantly they are comfortable! Not hard to find, often in the $20-30
                    range unless the militaria collector guys "have to have" them.

                    -Bill
                  • Bill M
                    ... Well, AES gets 16.50 for the Hammond xfmr (P-T156) + a 2.50 handling charge. Radiodaze sells it for 13.26 (HX124A) with no handling...plus daze has a
                    Message 9 of 13 , Apr 8 4:59 AM
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                      kyoritsu wrote:
                      > Hi Bill, I thought of ordering from Antique Radio, prices are all
                      > right, but the shipping is a killer. I'm going to keep my eyes open
                      > here for a suitable transistor amp transformer. It's good to know
                      > they should work.
                      >
                      > Rob

                      Well, AES gets 16.50 for the Hammond xfmr (P-T156) + a 2.50 'handling'
                      charge. Radiodaze sells it for 13.26 (HX124A) with no handling...plus
                      'daze has a lot more radio oriented parts if you're ready to bite the
                      shipping.

                      Are you located in Japan? I would think somewhere there might have
                      those Hammond xfmrs...but thats not to say they wouldn't cost an arm and
                      a leg locally.

                      Good luck,
                      Bill
                    • Larry Beaty
                      I find that hard to believe! Your experiments have always piqued my interest. On my side of the screen, you are very knowledgeable! You are certainly a go
                      Message 10 of 13 , Apr 8 7:03 AM
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                        I find that hard to believe! Your experiments have always piqued my
                        interest. On my side of the screen, you are very knowledgeable!



                        You are certainly a go getter to learn how things work, and very methodical
                        in your investigations.



                        I am one of your fans!



                        Btw, solid state is so simple. That's why I say simulate a transformer.
                        But I understand if you have never done any work in SS. I have spent my
                        whole life in SS. After that experience, it is so simple!



                        Larry



                        From: regenrx@yahoogroups.com [mailto:regenrx@yahoogroups.com] On Behalf Of
                        kyoritsu
                        Sent: Tuesday, April 08, 2008 2:34 AM
                        To: regenrx@yahoogroups.com
                        Subject: [regenrx] Re: more 3A5 twinplex experiments



                        Larry, I am a primitive when it comes to circuit design. I believe in tubes,
                        don't trust solid
                        state. However, I may try an interstage transformer meant for a transistor
                        amp. With low
                        voltage and current on the 3A5 detector, it might work.

                        --- In regenrx@yahoogroups.com <mailto:regenrx%40yahoogroups.com> , "Larry
                        Beaty" <hlbeaty@...> wrote:
                        >
                        > Just a little thought out of the box here. What if: you simulated a 3:1
                        > transformer with a solid state circuit just to see if it would work. I can
                        > understand cost! I think Mouser has some reasonably priced interstage
                        > transformers, but golly out where you live, shipping would be expensive!
                        >
                        >





                        [Non-text portions of this message have been removed]
                      • John Berry.
                        ... using. Pardon my ignorance, ... Mine are standard 16 ... yours. ... Phones,I notice you do use a output transformer with an 8 ohm output.The thought
                        Message 11 of 13 , Apr 9 3:46 AM
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                          --- In regenrx@yahoogroups.com, "kyoritsu" <rikkyograsing@...> wrote:
                          >
                          > Hi Bill M, I too have been thinking it's the stereo phones I'm
                          using. Pardon my ignorance,
                          > but what are R-14 phones? Old style cans? What's the impedance?
                          Mine
                          are standard 16
                          > ohm stereo phones, connected to a 10k to 8 ohm output transformer.
                          >
                          > I notice my breadboard layout is sort of a drunken version of
                          yours.
                          >
                          > Rob
                          >
                          >> Hi Rob.Not been following this item that close,but ref the stereo
                          Phones,I notice you do use a output transformer with an 8 ohm
                          output.The thought crossed my mind that IF you have connected the
                          Phones in Left/Right PARALLEL you are indeed matching the load on
                          the output tranny .Normal Stereo phones are NOT that sensitive,some
                          being not much difference than small loudspeakers !!.Here on this
                          side of the Atlantic the sought after headphones are the S.G.Brown
                          at around 5000 ohms,sometimes wired in series !!!,These are so
                          sensitive I've heard our local radio ststion VERY loudly using just
                          the Tip of the Jack Plug onto some steel racking (point contact
                          rectification !!!).John G1WOS.Bristol.UK.
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