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  • BEDROCK 1400

    Hey guys, been away for a while. So I have this Bedrock 1400 head on my bench. There's very little info on these amps, certainly no schematics that I can find. So my first question is, anyone have a schematic for this thing? And secondly, when the guy brought it in, he had blown tubes and had a bad input jack, and filter caps from 30 years ago. So I replaced these things. Didn't do anything crazy, just your typical maintenance. He brought it back 4 months later saying it stopped working. I once again have it on my bench. One of the 2 power tube sockets (EL34's) is eating tubes. I cannot for the life of me figure out why. The design of these things is pretty standard Fender/Marshall style, but laid out very tech-unfriendly and annoying. One thing I did notice was that the PT has a heater CT, and there is also an artificial/elevated CT on the power tube sockets. I disconnected the artificial CT resistors, but I can't tell if this has solved the problem. What happens if PT CT and artificial CT are used at the same time? And what else should I be looking at to understand why one tube keeps getting destroyed? Can Anyone shed ANY light on this? I'm happy to elaborate and provide pics and more info.

  • #2
    Pics and voltages.
    If there is only one secondary for all the heaters you only need one reference, be it ground or elevated, your choice.

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    • #3
      Here is what I have gathered up on the Bedrock amps.

      Bedrock.zip

      The drawing of the heater circuit shown on the 1400 is misleading.
      It is drawn a bit clearer on the 1200.

      Both show 100 ohm hum canceling resistors on the center tapped heater winding.

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      • #4
        My first suspect would be a bad contact on the grid 1 pin. Clean, retention and monitor the cathode current to see if it's fixed. The other possibility is that the socket is damaged from arcing. If that is the case replacement is the only option.

        The redundant heater resistors will have no affect on this.
        Experience is something you get, just after you really needed it.

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        • #5
          Check out these young rockers!

          Click image for larger version

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          • #6
            So those 100 ohm resistors can stay put, even though the heater wires have a CT?

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            • #7
              I'm unable to open that zip file

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              • #8
                Those resistors have been in there since the amp was built, so I don't see why you should worry about it. Also, the zip file opens fine for me so the problem must be on your end.
                "Yeah, well, you know, that's just, like, your opinion, man."

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                • #9
                  Cool. I'll check those things. I have extra tube sockets if it comes to that.

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                  • #10
                    The zip worked fine for me too. Maybe try it again.
                    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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