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Deluxe reverb Silverface Bad sound

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  • Deluxe reverb Silverface Bad sound

    I have a small problem with a Deluxe Reverb, it sounds a bit compressed and seems to have little power.
    The bias is well adjusted. But I see that there is more screen voltage than B +.
    I replaced the filter capacitors with F & T. And I have tried to replace the power valves without any positive results.
    I replaced the screen resistances with 4icon Xicon.
    If I turn on the amp without power valves, the B + voltage is higher than the Screen voltage. But with the valves installed the b + voltage is 413Vdc and the Screen Voltage is 415Vdc.
    This I think is not right.
    Attached image with voltages in power section.



  • #2
    There is nothing wrong with the measured voltages in your diagram. B+ is 418V and screens are at 415V. Plate voltages (413V) always are lower than B+ because of the voltage drop across the DCR of the primaries caused by the plate idle current. If you decrease idle currents, plate voltages and B+ will increase a few volts. If you read the legend (comments) in the schem, you find under item 1: "Values shown + or - 20%.
    - Own Opinions Only -

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    • #3
      Originally posted by Helmholtz View Post
      There is nothing wrong with the measured voltages in your diagram. B+ is 418V and screens are at 415V. Plate voltages (413V) always are lower than B+ because of the voltage drop across the DCR of the primaries caused by the plate idle current. If you decrease idle currents, plate voltages and B+ will increase a few volts. If you read the legend (comments) in the schem, you find under item 1: "Values shown + or - 20%.
      But I have a second Deluxe Reverb silverface and the plate voltage is 415Vdc and Screen Voltage is 415Vdc.
      In this amp the plate voltage is 413Vdc and screen voltage is 415Vdc . Is normal this?
      Regards

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      • #4
        Originally posted by binito View Post
        But I have a second Deluxe Reverb silverface and the plate voltage is 415Vdc and Screen Voltage is 415Vdc.
        In this amp the plate voltage is 413Vdc and screen voltage is 415Vdc . Is normal this?
        Regards
        Yes, your voltages are just perfect. The difference in plate voltages is 2V or 0.5%. Compare this to +/-20% allowed by Fender. In the other amp plate idle currents are probably a little lower.
        - Own Opinions Only -

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        • #5
          Originally posted by Helmholtz View Post
          Yes, your voltages are just perfect. The difference in plate voltages is 2V or 0.5%. Compare this to +/-20% allowed by Fender. In the other amp plate idle currents are probably a little lower.
          But should the voltage on the plates be higher than the voltage on the screens?not the opposite as I have

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          • #6
            Originally posted by binito View Post
            But should the voltage on the plates be higher than the voltage on the screens?not the opposite as I have
            No, it is no problem if screen voltage is a few volts higher than plate voltage at idle. Your values are completely normal. Things will change anyway when the amp is delivering output power.
            Absolutely no sense discussing a difference of 0.5%.
            - Own Opinions Only -

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            • #7
              Originally posted by Helmholtz View Post
              ...Plate voltages (413V) always are lower than B+ because of the voltage drop across the DCR of the primaries caused by the plate idle current. If you decrease idle currents, plate voltages and B+ will increase a few volts...
              @binito, have you tried reducing the idle plate current (ie via the bias control), as suggested above?
              The particular Vdc at which the plates and screen grids sit relative to each other will be determined by the OT primary leg resistances, the plate currents, the choke resistance, screen grid resistor resistances, and the screen grid currents.
              Perhaps compare those values of the 2 amps if you are bothered and want to find the root cause of the difference; but a couple of Vdc either way for either electrode at idle is immaterial, as with signal, the plate voltage will swing above and below the screen grid voltage.
              My band:- http://www.youtube.com/user/RedwingBand

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              • #8
                binito, Helmholtz is telling you the truth. You are worried over a volt or two, which is less than 1%. It may be preferable from an engineering sense to have screens substantially lower than plates, but this amp is perfectly normal. Your example makes my point: you have another amp where there is only a 2 volt difference. That is not a significant difference. It has already been pointed out that FENDER adds a note to the schematic that all voltages are +/-20%.
                Education is what you're left with after you have forgotten what you have learned.

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                • #9
                  "seems to have little power"

                  Have you measured the actual power output into a dummy load?

                  When you do, compare that to the other amplifier.

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                  • #10
                    Originally posted by binito View Post
                    I have a small problem with a Deluxe Reverb, it sounds a bit compressed and seems to have little power...
                    Maybe the speaker is crap; have you tried the amp through a different speaker?
                    My band:- http://www.youtube.com/user/RedwingBand

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                    • #11
                      I think I know why he is concerned, I've been there myself. He is thinking screens should always be lower than plate voltage, even if by a few volts, and since it is the opposite, it's a concern.
                      It's weird, because it WAS working fine.....

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                      • #12
                        Originally posted by Randall View Post
                        I think I know why he is concerned, I've been there myself. He is thinking screens should always be lower than plate voltage, even if by a few volts, and since it is the opposite, it's a concern.
                        But why? At large signal operation the screen voltage is higher than the plate voltage around half the time.
                        Last edited by Helmholtz; 09-08-2018, 10:31 PM.
                        - Own Opinions Only -

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                        • #13
                          Originally posted by binito View Post
                          I have a small problem with a Deluxe Reverb, it sounds a bit compressed and seems to have little power.
                          The bias is well adjusted. But I see that there is more screen voltage than B +.
                          What makes you say the bias is well adjusted?
                          You can adjust it so the plate voltage increases a bit (so it matches the numbers you get with the other amp). And it may sound less compressed too.
                          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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