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Reverb on Twin Reverb Reissue stopped working while playing

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  • Reverb on Twin Reverb Reissue stopped working while playing

    Hello everybody


    The reverb on my Twin Reverb Reissue stopped working yesterday right while I was playing. Things I've already checked :

    Green and black cables in reverb pan are properly soldered. Springs are ok. Reverb RCA cable is ok.
    Tubes are ok.
    If I bang on the amp, I can hear reverb, so I suppose V4 is working.

    Voltages on V3:

    Plate = 454 VDC
    Cathode = 8.3 VDC

    TP7 (R24 1M ohms, connected to Grid) = 0.08 VDC

    TP10 (Reverb Transformer Green and Black) = 0.1 mvdc
    TP11 (R26, connected to grid on V4) = 0.1 mvdc

    Someone suggested testing the reverb transformer with an 8 Ohm speaker, but I don't have such a speaker lying around. It's also worth mentioning that when reverb and vibrato are on at the same time the amp makes a noise resembling the one of a helicopter. When the reverb is off, tremolo works perfectly.

    Any ideas ? Do the voltages seem ok ? Thank u.

  • #2
    No voltages on V3 are not OK
    open cathode resistor maybe= 8.3VDC or a bad 12AT7...

    The reverb return is working but i think the reverb send is disabled.
    I think your cathode should read 5 volts.
    Last edited by soundguruman; 01-19-2014, 12:41 PM.

    Comment


    • #3
      soundguruman, you mean that when the resistor is open it reads 8.3 VDC ?

      Comment


      • #4
        Yes, you got something going on in the reverb drive that disables the drive tube.
        The 1.5 k resistor is no longer 1.5K? or the tube is bad?

        Comment


        • #5
          The resistor connected to the cathode of V3 is according to the schematics a 2.2 K resistor. Mine is exactly the same and resistance reads 2.180. I've checked for continuity and R25 is properly connected to R24, C14 and pins 3 and 8. Click image for larger version

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          Comment


          • #6
            Originally posted by belf View Post
            The resistor connected to the cathode of V3 is according to the schematics a 2.2 K resistor. Mine is exactly the same and resistance reads 2.180. I've checked for continuity and R25 is properly connected to R24, C14 and pins 3 and 8. [ATTACH=CONFIG]27043[/ATTACH]
            Well, seems like I was looking at a different schematic, BUT...
            Your plate reads 454 volts, and it should be 67 volts...
            so the tube is shut off somehow.
            So, a bad socket, a bad wire, a bad tube, etc...? is the filament ON?
            Yeah, the tube should be dropping that voltage, if it's ON.
            So something has got the reverb drive shut off....is the reverb drive transformer primary winding shorted?

            Comment


            • #7
              I was reading a similar a topic here on the forum : http://music-electronics-forum.com/t9713/

              he signal feeding the reverb drive is split off and routed through a 500pf cap. C13 in your reissue Twin. Is it good and properly soldered?
              If the 12AT7 cathode resistor, R25 is open the circuit won't work.
              Likewise, if the cathode bypass cap, C14, is shorted the circuit won't work.
              The DC voltage on pins 3 & 8 should be about ~8 to 9V.
              The plate voltage should be ~400 to 450.


              I know the schematics says 67v, but is it really correct ? I'm simply measuring it with my meter set on DC. Besides, I'm running the amp with only 1 speaker and 2 output tubes and I'm in Europe, so I guess that might also affect the voltages ?

              Comment


              • #8
                The TP voltages that are in a 'rectangle', are measured in volts dc.
                These are for static test voltages.

                The TP's in an 'oval' are to measured in volts ac.
                These are for dynamic test voltages (ie: with a signal applied)

                You need to determine if the reverb pan is o/k.
                Measure the resistance of the input & output jacks of the pan itself.
                Then connect the wires at the tank & measure them at the amp end.
                They should read the same.

                Comment

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