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DSL 50 Cathode follower voltage

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  • DSL 50 Cathode follower voltage

    Hey all, I have a DSL 50 on the bench, cathode follower tube V3 is shot. It was a brand new JJ ECC83. Voltage at this socket is high, pin 1 is 390V. Also measured
    Pin 2, 216v
    Pin 3, 228v
    Pin 6, 215v
    Pin 7, 0v
    Pin 8, 1v

    Should I be concerned with the voltage at pin 1 and what tube should I use?

  • #2
    Those voltages are in the ballpark for the cathode follower.
    The problem is with the heater to cathode spec of the tube. Heater is around zero volts, cathode of first half is at 228V. Lots of preamp tubes have trouble with this.
    It seems to especially be a problem with spiral filament tubes, so you don't want one of those in that spot.
    Maybe someone here will have a brand & model recommendation for the cathode follower.
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


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    • #3
      Thanks. I am aware of not using spirals in this position. The cathode voltage concerns me too, it seems every new production tube is not up to the task at hand. I am considering a NOS tube, I have heard just a Chinese does well here too. Maybe a voltage drop is warranted? I believe a 4.7k 1w feeds that circuit B+.

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      • #4
        That 4k7 (if you mean R61) drops the voltage to the stages ahead (V1 & V2). R62, 1K 1W sets the voltage for V3, but would also affect V1 and V2, so I don't think that is a good method.
        Attached Files
        Originally posted by Enzo
        I have a sign in my shop that says, "Never think up reasons not to check something."


        Comment


        • #5
          I was going off memory, looking at the schem I see that now. All other tubes are fine, so don't want to change those really. I have a TAD 12AX7-C in there now, see what happens.

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