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Ten Tec 1253 Mods

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  • kb0add
    Greetings to one and all, I am not the new kid on the block but this is my first post. I am building a Ten Tec 1253 Receiver and have planed to put a few mods
    Message 1 of 9 , Jun 1, 2010
      Greetings to one and all,

      I am not the new kid on the block but this is my first post. I am building a Ten Tec 1253 Receiver and have planed to put a few mods in it. I have a question or two about two of them.

      I am going to be adding an external frequency counter. I have an FCC 1 in a stand along box and plan on using it. My question is where do I hook it up on the inside? Most of the time they say "put in a few turns at the end of the cord and hook it around the main coil. That sounds great, except, there is NO main coil.

      I am also going to replace the one turn main tuning pot with a 10 turn pot. Has anyone tried this and how does it work?

      Thanks in advance for your answers, and they will be greatly appreciated.

      John Kinnunen
      KB0ADD
    • kyoritsu
      Hi John. I did try a 10 turn pot for the main tuning but went back to a standard type. The 10 turn pot I used gave an odd stepped tuning response. That is,
      Message 2 of 9 , Jun 2, 2010
        Hi John. I did try a 10 turn pot for the main tuning but went back to a standard type. The 10 turn pot I used gave an odd 'stepped' tuning response. That is, when the 1253 was oscillating, as I zeroed in on the carrier of a signal, the heterodyne beat was actually a series of close but discrete, separate tones. Not a trombone slide. But I don't know if all 10 turn pots do this.

        Another thing: I didn't like the tiny ten turn knob and counter that came with the pot. A tuning knob should be at least an inch and a half in diameter. Tried a larger knob but that obscured the counter.

        Something else: with the original linear taper pot, the low end of each band is very compressed, the high end very expanded (with emphasis on the word 'very'). I tried an audio taper pot to better balance the tuning, but got a very flat area in the middle. Audio taper pots sometimes simply use two linear tracks that intersect to approximate the audio taper, and that's what caused it. A true audio taper might work very nicely.

        One suggestion: don't use those tiny, crappy 10k pots TenTec provides. Use quality pots. I know it's not easy to fit a larger pot on that small PCB, but it's easier to do it now. Sad voice of experience.

        No experience with a frequency counter.

        Rob




        --- In regenrx@yahoogroups.com, "kb0add" <kb0add@...> wrote:
        >
        > Greetings to one and all,
        >
        > I am not the new kid on the block but this is my first post. I am building a Ten Tec 1253 Receiver and have planed to put a few mods in it. I have a question or two about two of them.
        >
        > I am going to be adding an external frequency counter. I have an FCC 1 in a stand along box and plan on using it. My question is where do I hook it up on the inside? Most of the time they say "put in a few turns at the end of the cord and hook it around the main coil. That sounds great, except, there is NO main coil.
        >
        > I am also going to replace the one turn main tuning pot with a 10 turn pot. Has anyone tried this and how does it work?
        >
        > Thanks in advance for your answers, and they will be greatly appreciated.
        >
        > John Kinnunen
        > KB0ADD
        >
      • Hue Miller
        As usual, good thinking, Rob, and a useful post. I will now look more critically at those Knobpots I have saved up. ( The 10 turn pots with built in
        Message 3 of 9 , Jun 2, 2010
          As usual, good thinking, Rob, and a useful post. I will now look more critically at those
          "Knobpots" I have saved up. ( The 10 turn pots with built in mechanical digital counter
          in the knob ). Because of their rather small size. The stepped function you experienced
          is not, I think, typical.

          The most common way to pick off signal for the freq counter is to use one or two
          transistors, with the input one an FET, to pick off a sample of the RF voltage with
          minimum loading. I am certain I have seen this in one or two QRP or regen circuits
          published, but can't name a source at this instant, but I'm sure he can find one.

          One or more of the old WW2 US Navy regen type receivers had an "oscillator test"
          button. The builder might want to have something like this to set the regen into
          oscillation when the frequency counter is needed (assuming the input signal
          is normally too small to reliably trigger the freq counter).
          -Hue

          [Non-text portions of this message have been removed]
        • W3FIS
          I have posted a file on this group concerning the TT1253... Major mod I made was to put a UHF connector on the back, and replace the ground and antenna
          Message 4 of 9 , Jun 2, 2010
            I have posted a file on this group concerning the TT1253... Major mod I made was to put a UHF connector on the back, and replace the ground and antenna connections with a good pair of binding posts. Also, used the extra on/off switch connection to short the input when the power was off. Otherwise, "stock." I borrowed an antenna analyzer to use as a frequency source for calibration, put the points into an Excel spreadsheet, and set them up as graphs, printed them out on a small card, and keep it with the receiver. Also, I put a piece of window screen over the loudspeaker to keep junk out of it.

            /paul W3FIS
          • Larry Beaty
            Smart work. Little things that put YOU into the radio. Congratulations! Larry From: regenrx@yahoogroups.com [mailto:regenrx@yahoogroups.com] On Behalf Of
            Message 5 of 9 , Jun 2, 2010
              Smart work. Little things that put YOU into the radio. Congratulations!



              Larry



              From: regenrx@yahoogroups.com [mailto:regenrx@yahoogroups.com] On Behalf Of
              W3FIS
              Sent: Wednesday, June 02, 2010 11:51 AM
              To: regenrx@yahoogroups.com
              Subject: [regenrx] Re: Ten Tec 1253 Mods





              I have posted a file on this group concerning the TT1253... Major mod I made
              was to put a UHF connector on the back, and replace the ground and antenna
              connections with a good pair of binding posts. Also, used the extra on/off
              switch connection to short the input when the power was off. Otherwise,
              "stock." I borrowed an antenna analyzer to use as a frequency source for
              calibration, put the points into an Excel spreadsheet, and set them up as
              graphs, printed them out on a small card, and keep it with the receiver.
              Also, I put a piece of window screen over the loudspeaker to keep junk out
              of it.

              /paul W3FIS





              [Non-text portions of this message have been removed]
            • W3FIS
              The UHF connector on the back also nicely allows me to mount a Miracle Whip antenna.. /paul W3FIS
              Message 6 of 9 , Jun 2, 2010
                The UHF connector on the back also nicely allows me to mount <gasp> a Miracle Whip antenna..

                /paul W3FIS
              • davidpnewkirk
                ... From the 1253 schematic I think the first tap point to try is the source of detector transistor Q3--the junction of C6 (0.01 uF), L10 (100 uH), and R6 (100
                Message 7 of 9 , Jun 2, 2010
                  --- In regenrx@yahoogroups.com, "kb0add" <kb0add@...> wrote:

                  > I am going to be adding an external frequency counter.
                  > I have an FCC 1 in a stand along box and plan on using it. My
                  > question is where do I hook it up on the inside? Most of the time
                  > they say "put in a few turns at the end of the cord and hook it
                  > around the main coil. That sounds great, except, there is NO main
                  > coil.

                  From the 1253 schematic I think the first tap point to try is the source of detector transistor Q3--the junction of C6 (0.01 uF), L10 (100 uH), and R6 (100 kilohms).

                  I see from the FCC-1 page at http://www.norcalqrp.org/fcc1.htm that the counter's input impedance is 1 megohm in parallel with 15 pF, and that it will need in the vicinity of 30 mV rms to count--a pleasantly low value from the standpoint of success being likely. :-) So as a start I recommend coupling the counter input (or the counter jack you add to the front or rear panel of your 1253 by as short a lead/cable as possible) to the source of Q3 via a 22 or 33 pF capacitor. Assuming that you'll add a counter jack to the receiver, keep the shielded cable between it and the receiver short as well.

                  The short shielded cable you use between the receiver and counter will add shunt capacitance and so reduce the signal supplied to the counter, and so you may want to add a JFET source follower amplifier between Q3 and the counter to reduce the impedance of the feed between the receiver and counter, but try it the simpler way first.

                  Best regards,

                  Dave
                  amateur radio W9VES
                • Richard Brunner
                  When using the RAK and RAL receivers sometimes it s hard to tell whether the detector is oscillating or not because of noise, etc, so the test button
                  Message 8 of 9 , Jun 4, 2010
                    When using the RAK and RAL receivers sometimes it's hard to tell whether
                    the detector is oscillating or not because of noise, etc, so the test
                    button momentarily stops it, and you hear a "click" when you release the
                    button as it goes back into regeneration. No regeneration, no click or
                    pop.

                    Richard
                    >
                    > One or more of the old WW2 US Navy regen type receivers had an
                    > "oscillator test"
                    > button. The builder might want to have something like this to set the
                    > regen into
                    > oscillation when the frequency counter is needed (assuming the input
                    > signal
                    > is normally too small to reliably trigger the freq counter).

                    >
                  • davidpnewkirk
                    ... That s an excellent idea. One aspect I left out of my earlier post is that depending the type of signal received and how it s received, we may be using a
                    Message 9 of 9 , Jun 5, 2010
                      --- In regenrx@yahoogroups.com, "Hue Miller" <kargo_cult@...> wrote:

                      > One or more of the old WW2 US Navy regen type receivers had an
                      > "oscillator test" button. The builder might want to have something
                      > like this to set the regen into oscillation when the frequency
                      > counter is needed (assuming the input signal is normally too small
                      > to reliably trigger the freq counter).

                      That's an excellent idea. One aspect I left out of my earlier post is that depending the type of signal received and how it's received, we may be using a regenerative detector below the threshold of oscillation. When this is so, the drive provided by the detector to an external counter may be chaotic at best, possibly leading to instability of the displayed frequency as the counter tries to make sense of the input. A momentary switch to pop the detector into full oscillation, a la the RAK/RAL, would solve that problem. (Preceding the counter by a limiter could also work, but possibly introduce other problems; see the next paragraph.)

                      A possible drawback of connecting a counter anything like directly to the input of a sensitive receiver--and a practical regen certainly qualifies--may be the introduction of digital noise from the counter circuitry. A buffer stage with high reverse isolation may be necessary if that happens. I have a two-BJT-cascode such circuit I can suggest--on paper, it exhibits something like 80 to 100 dB of reverse isolation--but will wait to see how the simpler approach works.

                      Best regards,

                      Dave
                      amateur radio W9VES
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