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Redplate Ceriatone 20w Lead Bass / Marshall 2061

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  • Redplate Ceriatone 20w Lead Bass / Marshall 2061

    Can someone help me with next steps here?

    bought this "amazing build" but it was redplating

    So i'm reading that this is a common issue with this model? Crazy voltages and redplating, now slightttt (have to go to a dark room) but still there. The transformer should be spec'd correctly based on the layout showing the 290 for primary, i'm getting like 300 there , so not really sure why everything is so high. Model used here is PT -290-50 HT-6179-50

    So far i've upped the sag resistor from 22 ohm to 34 ohm, the bias resistor is now at 165 ohms

    DCV Pins with Tubes giving the same readings
    1 N/A
    2 V1 - 26mv, v2 33mv
    3 14.18V
    4 .2mv
    5 0
    6 N/A
    7 375v
    8 N/A
    9 382v

    If i go up to like 210 ohms for the bias resistor, will that kill the plate voltages?

    whats next steps here?

    love the sound of the circuit, seems like im close here but worried about upping the b+?
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  • #2
    "If i go up to like 210 ohms for the bias resistor, will that kill the plate voltages?"

    Plate voltages will go lower.
    Not sure what you mean by 'kill'.

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    • #3
      sorry for the wording, i thought increasig the bias resitor would hike up the b+ which would be bad

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      • #4
        If i go up to like 210 ohms for the bias resistor, will that kill the plate voltages?
        If you increase the common EL84 cathode resistor (shown as 125R in the layout), idle current will be lower and B+ will increase because of lower PS load.
        - Own Opinions Only -

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        • #5
          Originally posted by Helmholtz View Post
          If you increase the common EL84 cathode resistor (shown as 125R in the layout), idle current will be lower and B+ will increase because of lower PS load.
          right so what's my next step here increase to 210 ohms for the cathode resistor? will that much b+ be tolerable? or where in the circuit do i need to adjust to stop these guys from redplaing

          Comment


          • #6
            Originally posted by trip View Post
            right so what's my next step here increase to 210 ohms for the cathode resistor? will that much b+ be tolerable? or where in the circuit do i need to adjust to stop these guys from redplaing
            What is the voltage across the 165R cathode resistor?
            - Own Opinions Only -

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            • #7
              14.23 DC v

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              • #8
                Originally posted by trip View Post
                14.23 DC v
                THat means 43mA cathode current per tube. Somewhat high. But your main problem is high B+ and screen voltages. To bring down B+ to a safer value you will need something like a 330R/10W sag resistor or a 33V to 50V/10W power zener diode.
                - Own Opinions Only -

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                • #9
                  It will have horrible crossover distortion if the cathode resistor is increased too much. It's better to reduce plate dissipation by reducing plate voltage not current (as Helmholtz said) I use a 220R 10W sag resistor and 150R cathode resistor.

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                  • #10
                    Cathode current will drop with lower screen voltage.
                    - Own Opinions Only -

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                    • #11
                      Originally posted by Helmholtz View Post
                      Cathode current will drop with lower screen voltage.
                      so is thst my best bet? I don't want to be just guessing i figured there'd be a math formula to figure this out

                      i need to go back to like 150 ohm for the bias resistor but increase the sag resitor from 30ohm to something like 220ohm ? is'nt this going to affect the tone a lot, why would it be sooo off spec from the layout

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                      • #12
                        What is your line voltage? What is the heater voltage?
                        "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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                        • #13
                          121.8, 3.31v

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                          • #14
                            Click image for larger version

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                            • #15
                              Originally posted by trip View Post
                              [ATTACH=CONFIG]58538[/ATTACH]
                              Well Iím getting 121 out of the wall or from hot to ground on the iec but from the iec hot to Star ground point I get 108

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