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Fender Custom Vibrolux Reverb - PT problem

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  • Fender Custom Vibrolux Reverb - PT problem

    https://www.thetubestore.com/lib/the...-Schematic.pdf

    Schematic ^^^

    Hello, my buddy has the amp in question, from the very late 90s, and we believe his PT has failed. The amp just shut itself off quick and clean without any fireworks or drama. Just...dead. The fuse is still intact, nothing is burnt or fried, it just went dead. He's in Austin, TX, I'm in Houston, so I'm "diagnosing" his amp through texts and over the phone while he takes rudimentary measurements at my instruction. But it seems like the primary winding of his PT has gone open.

    My question is in finding a suitable replacement. The part # of his existing transformer is B-036958. If you look up that part number it brings you to a PT for a Hot Rod Deluxe, which has half the number of preamp tubes that the Vibrolux Reverb does.
    120 VAC @ 60 Hz (Black - White)
    495 VDC unloaded, 440 VDC @ 65.7 mA DC, 388 VDC @ 200 mA DC
    53.6 VAC @ 1.58 A AC
    6.6 VAC @ 3.75 A AC

    Are those specs enough voltage and amps for a six 12AX7, two 6L6 amp?

  • #2
    Check the heater current i.e. add up all the heater currents from that schematic and see if it's adequate, that's usually the limiting factor. Generally a 12AX7 only draws 1mA or so of HT current, so likely not an issue for overloading a 6L6 amp.

    Comment


    • #3
      Originally posted by Greg_L View Post
      Are those specs enough voltage and amps for a six 12AX7, two 6L6 amp?
      Yes.

      - Own Opinions Only -

      Comment


      • #4
        Correct me if I'm wrong here...

        A 12AX7 consumes about .3 amps per tube for the heaters, right?
        A 6L6 consumes about .8a per tube?
        That's 3.4 amps heater current on the 6.3v winding...
        That's within spec but it's pretty close.

        I'm also concerned about the B+. It says 440 or 388 VDC depending on the amp draw? I don't understand that part. What makes the difference between it having 440v or 388?

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        • #5
          6L6GC .900a so total would be 3.6A. It may be close but many manufacturers would even go higher and use the entire 3.75A.

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          • #6
            Originally posted by Greg_L View Post
            What makes the difference between it having 440v or 388?
            The increased current demand at full output (200mA) makes B+ sag compared to idle.
            The voltages specified correspond to what I measured with my SF Vibrolux Rev.

            It is normal that B+ drops by 10% to 15% at full output.

            - Own Opinions Only -

            Comment


            • #7
              Ok great thanks everyone. I understand better now.

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