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Why Does The Output Tube On My Vibro Champ Not Stay Lit?

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  • Why Does The Output Tube On My Vibro Champ Not Stay Lit?

    I have made mods on my amp, 3 prong plug, Mercury Magnetics output transformer, 10 inch speaker mod, 5V4 rectifier for slower warm up and 5881 output tube. When I play, everything sounds and performs beautifully until the sound fades and then drops out. When I look at the tubes, all the filaments are lit except the output tube. Any ideas?

  • #2
    Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

    A bad connection, maybe a valve pin. Try reseating/reinserting the valve. Use some contact cleaner on the pins.
    sigpic

    - http://www.soundclick.com/bands/defa...?bandID=804435 -
    - https://soundcloud.com/mr-ds-bigband/tracks -

    Warning: May contain traces of NUTS

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    • #3
      Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

      Originally posted by GoldenVulture View Post
      A bad connection, maybe a valve pin. Try reseating/reinserting the valve. Use some contact cleaner on the pins.
      I had changed the tube and the same thing happened. I did spray the tube pins with contact cleaner. Perhaps I need to tighten the socket contacts.

      Thank you Golden Vulture.

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      • #4
        Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

        If it continues to happen maybe reflow the heater wire connections on the valve socket pins. Possibly a dry joint that plays up when it gets a bit of heat in it.
        sigpic

        - http://www.soundclick.com/bands/defa...?bandID=804435 -
        - https://soundcloud.com/mr-ds-bigband/tracks -

        Warning: May contain traces of NUTS

        Comment


        • #5
          Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

          I have already reflowed the solder on the wire/connection for the filament output tube socket. Thank you for your replies.

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          • #6
            Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

            Is it wired with solid core wire?

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            • #7
              Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

              Originally posted by Darg1911 View Post
              Is it wired with solid core wire?
              I'm not sure about solid core wire. I believe it is the original filament wire.

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              • #8
                Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                I've seen the solid core broken under the insulation but it still work intermittently. I imagine that it could also happen with stranded. If it's the filament in one power tube it pretty much has to be either the wire feeding that tubes heater or the socket. Otherwise, it would be happening with the other tubes. Unless, maybe, the problem tube is the last tube in the circuit. Then it could be a bigger problem. Have you checked filament voltage? I'd check at the problem tube and the rest of them as well. Note that I'm not a tech, this is just what comes to mind. I just know enough to be dangerous yet unlikely to electrocute myself.
                Last edited by Darg1911; 02-11-2018, 12:52 PM.

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                • #9
                  Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                  Your input is greatly appreciated, thank you. I will probably have to wait until tomorrow to pull the chassis out and recheck everything. I might try some contact cleaner in the tube socket to see perhaps a quick fix.

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                  • #10
                    Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                    While you have it out, may as well also try and re-tension the contacts in that one socket. If a loose contact is the problem, tightening up may work. Well, at least until the tube gets pulled another time or two. Cant hurt anyway. Just make sure the caps are discharged before you go poking around (I know that you know this already).

                    Good luck. Please report back.

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                    • #11
                      Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                      Another couple thoughts. If you know for sure that it definitely is not the tube, focus on the socket. The power tube filaments should be first off the power tranny which would rule out the wires as they would affect the downstream 9 pin tubes as well.

                      You swapped to a 5881 which draws twice the heater current as the 6v6. I don't know what the current rating is for the filament winding on the power tranny but thought I would mention it as well.

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                      • #12
                        Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                        Originally posted by Darg1911 View Post
                        Another couple thoughts. If you know for sure that it definitely is not the tube, focus on the socket. The power tube filaments should be first off the power tranny which would rule out the wires as they would affect the downstream 9 pin tubes as well.

                        You swapped to a 5881 which draws twice the heater current as the 6v6. I don't know what the current rating is for the filament winding on the power tranny but thought I would mention it as well.
                        If the heater current draw was more than the power transformer could handle.........wouldn't that affect ALL the filaments on every tube? I am unable to verify but I thought I read somewhere that the power transformer for a Vibro Champ was over rated for voltage/amperage.

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                        • #13
                          Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                          I have other issues. I brought in 2 NOS 5881s and 2 NOS 6V6s and I installed the first 5881. Both the output and power transformers got hot. I then removed and replaced the 5881 with another and the filament wouldn't light. I then installed the first 6V6 and it started to red plate. I removed the 6V6 and replaced with another and the filament wouldn't light. What is going on? This thing is driving me crazy.

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                          • #14
                            Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                            The Vibro is cathode biased. You replaced the output transformer. I don't recall what desired output impedances are for the 6v6 and the 5881, but off hand, I think it works as long as the bias is adjusted accordingly. I would suspect that your one 6v6 redplating would be due to it being biased too hot. Just because one 6v6 red plated doesn't mean the other will do the same. Try to find data on your power transformer and see what it's ratings are. Make sure you aren't exceeding with the 5881. The extra half amp or so is probably ok but you never know. You still need to check the voltages on all the tubes filaments. If you are having intermittent problems with multiple power tubes in terms of the filaments not lighting up, it could just go back to the socket (or wire if, for some reason, the power tube is last in line on the filament circuit). Again, I'm not a tech but I'm not sure that a good tech could diagnose whatever is going on over the internet. You could have multiple problems related to the socket, the tubes, the transformer (specs wise anyway), bias. Start measuring voltages, poke around with a chopstick and see if anything jumps out at you. Double check the wiring. Check the bias. And don't get electrocuted.

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                            • #15
                              Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

                              I fixed the intermittent filament issue on the output tube......open/connection on the filament/ground on the output tube socket. I replaced the tubes with a 5Y3 and another 6V6 and I still get a red plate condition. What value of resistor do I need to change for the cathode bias? Thank you for your help.
                              Last edited by Jeffblue; 02-12-2018, 03:58 PM.

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