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  • #61
    Thanks for the answer. Yes I have replaced the bridge and all power caps to 4x47MF. No hum at all.
    Yesterday I had a short test with a new tape and it seems that the unit is okay.
    One interesting thing is that the "magic eye" which is about a half millimeter slice without sound. If I play music at maximum peak, it only widen to about 3 millimeters not more.
    Is there any trimmer pot to adjust the "magic eye" circuit signal input? Or the tube is faulty?

    https://www.youtube.com/watch?v=6O0G-LsTk6Q

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    • #62
      There is no adjustment and the tube is not faulty.
      As I said in my last reply you should replace all those small capacitors..0047, .022 etc
      Which model do you own, does it have a printed circuit board or are the small parts wired to tag strips, there are some differences in the circuitry and the ease in which components can be replaced.

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      • #63
        Hello Mickey,
        I have the one, with circuit board. Yes it would be nice to replace all caps. but i guess I will not dis-montage the unit.
        I fear that some or more wire will break (as I experienced already during fault analysis).
        So now the unit works and does its function as expected after 50 years.
        Thanks,

        Comment


        • #64
          Originally posted by Mickey View Post
          There is no adjustment and the tube is not faulty.
          As I said in my last reply you should replace all those small capacitors..0047, .022 etc
          Which model do you own, does it have a printed circuit board or are the small parts wired to tag strips, there are some differences in the circuitry and the ease in which components can be replaced.
          Hi Mickey,
          I have noticed that you are an expert for repairing Echolette NG51S echo units. I have an Echolette NG51 S my model is with a printed circuitboards, everything works perfectly, transportation system all five magnetic heads have 1.2 KOhm resistance a ‘Dry’ signal is crisp and without any hum, I checked two playback heads by gently teaching them with a screwdriver and they work, I can hear them via my guitar amplifier.

          However, I cannot get any echo sound. I measured the voltage on the variable caps and I got low voltage result. Head 1 has 20 Volts, Head 2 had 30 Volts and Head 3 approx 44 Volts all voltages have 65KHz frequency. The erase head has only 20 Volts!?

          Is it possible that the high friquency oscillator is not working or should I check something else?
          Thank you in advance,
          Sinisa

          Comment


          • #65
            Originally posted by Sin1949 View Post

            However, I cannot get any echo sound. I measured the voltage on the variable caps and I got low voltage result. Head 1 has 20 Volts, Head 2 had 30 Volts and Head 3 approx 44 Volts all voltages have 65KHz frequency. The erase head has only 20 Volts!?

            Is it possible that the high friquency oscillator is not working or should I check something else?
            I'd say 65kHz is your oscillator frequency, so it's working.

            I guess you used a scope for the measurements?

            Are all switches working properly?
            - Own Opinions Only -

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            • #66
              Hi Helmholtz,


              Yes, I used a digital scope and high quality Fluke multimeter and I got 65KHz oscillator frequency measuring on the three variable capacitors connected to recording heads.

              I know that the voltage on the recording heads should be in. the range of 40Volts for Head 1, 70Volts Head 2 and 90Volts for Head 3.

              So my question is: Let say, consider that the high frequency oscillator is working how to bring up the Voltage on three recording heads? Also I checked the ECC82 oscillator tube and it is working properly.

              All the switches are working properly.

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              • #67
                Where do the reference HF voltages come from?

                Are you sure you're not comparing RMS values with peak-to-peak values?

                Did you ever measure your HF voltages before this failure?
                Last edited by Helmholtz; 11-11-2021, 01:19 PM.
                - Own Opinions Only -

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                • #68
                  I measured the Voltage/Frequency at the three variable capacitors located at the right hand side of the chassis looking at the face plate of the echo unit. I did not measure Voltage/Frequency before.

                  Also when I connect the echo unit with the guitar amplifier and when I am touching the connectors of those three variable capacitors I can hear a sound (screeching sound) from the amplifier. That is telling me that there is some ‘life’ connection between the variable capacitors and echo unit exit.
                  Last edited by Sin1949; 11-11-2021, 06:46 PM.

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                  • #69
                    Please answer my other 2 questions above.

                    I'm not convinced that the HF levels are your root problem.
                    - Own Opinions Only -

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                    • #70
                      Originally posted by Helmholtz View Post
                      Please answer my other 2 questions above.

                      I'm not convinced that the HF levels are your root problem.
                      I measured the Voltage directly from the variable capacitors which is the RMS Voltage.
                      At least I think so, as I remember that the Peak Voltage should be calculated by formula 2x square root of RMS

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                      • #71
                        Originally posted by Sin1949 View Post
                        I measured the Voltage directly from the variable capacitors which is the RMS Voltage.
                        How do you know?

                        A sine voltage can be specified as RMS value Vrms, peak value Vp = 1.4 Vrms or peak-to -peak value Vpp = 2 Vp = 2.8 Vrms.
                        DMMs typically measure RMS value.
                        With a scope you typically read Vpp.

                        HF voltages in schematics/manuals are often specified as Vpp.

                        So again my question: Where did you find the reference HF voltages? Can you post your source?
                        Last edited by Helmholtz; 11-11-2021, 08:21 PM.
                        - Own Opinions Only -

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                        • #72
                          Originally posted by Helmholtz View Post

                          How do you know?

                          A sine voltage can be specified as RMS value Vrms, peak value Vp = 1.4 Vrms or peak-to -peak value Vpp = 2 Vp = 2.8 Vrms.
                          DMMs typically measure RMS value.
                          With a scope you typically read Vpp.

                          HF voltages in schematics/manuals are often specified as Vpp.

                          So again my question: Where did you find the reference HF voltages? Can you post your source?


                          So, here I am again I checked again the Voltage/Frequency using my digital Scope.

                          The frequency was 57.3KHz at the Head1 the Vpp = 101.56Volt; Vmax= 50.6Volt and Vmin= 50.9Volt
                          Interesting the same Voltage/Frequency I measured on the H 2.
                          However, I am sure that the Voltage on H 2 I can fine adjust to different values.


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                          • #73
                            Originally posted by Sin1949 View Post
                            The frequency was 57.3KHz at the Head1 the Vpp = 101.56Volt; Vmax= 50.6Volt and Vmin= 50.9Volt
                            Interesting the same Voltage/Frequency I measured on the H 2.
                            However, I am sure that the Voltage on H 2 I can fine adjust to different values.
                            These values don't look consistent with your earlier measurements.

                            Some more info here: https://music-electronics-forum.com/...tte-klemt-ng51

                            Judging from the variable cap values HF bias should increase from head 1 to head 3.

                            But I don't think wrong HF voltages are the reason for your missing echo sound.
                            So you need to do real troubleshooting.
                            Start with measuring tube DC voltages and post them.
                            Then feed a 100mV/1kHz signal to an instrument input and trace it to the record level controls.

                            There is useful info earlier in this thread.

                            Be prepared to replace a tube.
                            Last edited by Helmholtz; 11-13-2021, 06:25 PM.
                            - Own Opinions Only -

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                            • #74
                              Originally posted by Helmholtz View Post

                              These values don't look consistent with your earlier measurements.

                              Some more info here: https://music-electronics-forum.com/...tte-klemt-ng51

                              Judging from the variable cap values HF bias should increase from head 1 to head 3.

                              But I don't think wrong HF voltages are the reason for your missing echo sound.
                              So you need to do real troubleshooting.
                              Start with measuring tube DC voltages and post them.
                              Then feed a 100mV/1kHz signal to an instrument input and trace it to the record level controls.

                              There is useful info earlier in this thread.

                              Be prepared to replace a tube.
                              Thank you for the quick response. Yes you are absolutely right, the results are not consistent because in the mean time I have adjusted/tuned the variable capacitors and the trim resistors. Also I used then my old analog Tektronix 2212 scope and Fluke multimeter and I got obviously the half of the Vpp.

                              But I will change the Voltage setting and now I am using Hantek Digital scope which is reading automatically the Voltage and Frequencies.

                              As I know the HF bias should be be 60Volt at H1, 90Volt at H2 and 120Volt measured at H3.
                              The erase head should be approx 70Volt.

                              Tonight I will measure all the points that you mentioned. Soon after I will post the results.
                              Best Regards from rainy Vancouver, BC, Canada

                              Comment


                              • #75
                                Originally posted by Sin1949 View Post

                                As I know the HF bias should be be 60Volt at H1, 90Volt at H2 and 120Volt measured at H3.
                                The erase head should be approx 70Volt.
                                I already asked several times: What is your source? And are these Vpp or Vrms values, as the difference would be almost a factor of 3?
                                Last edited by Helmholtz; 11-13-2021, 11:32 PM.
                                - Own Opinions Only -

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