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Sweetening 5E3 overdrive

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  • Sweetening 5E3 overdrive

    I work on guitar amps, but my background is as a keyboard player. I've got a client who bought a 5E3 kit built by someone else (a Weber kit, I think), and he asked me to de-bug it. He thought that there was a problem with the speaker, but that turns out not to be the case. The scope shows me that what he doesn't like about the amp is that it has a kind of unpleasant overdrive tone, which he perceived to be a speaker malfunction. Swapping different speakers makes no difference.

    I've tamed it somewhat by adding a grid-stopper resistor to the input of the phase inverter, but it still has a kind of "ragged" sound when driven hard. And, because it's only 14 Watts, it's easy to drive hard. I've had to explain to the client that this amp is very different from his DRRI, despite it being a Fender circuit and having a 2 x 6V6 output section.

    So, I'm wondering: what is the great appeal of the 5E3 design? I've heard other 2 x 6V6 amps from this era, like the Multivox Premier 120 that seem to sound better "out of the box," without a lot of tweaks and mods. Or is successful tweaking and modding part of the fun of building one of these? :-)

    All that said, any further tips on how to make this amp sound a bit sweeter when overdriven? I've been through it carefully, and there's absolutely nothing "wrong" with it. It's just the circuit itself. Is this where the Paul Ruby zener mod might come in handy?
    Thanks in advance for any advice!

    P.S. Coupling caps are all 0.022uF Sozos, and we have played with cathode bypass values without success.

  • #2
    How big did you do with the grid stopper? 1M is fine, won't cut treble (due to there being no voltage gain) and may help to smooth it out.
    My take is that because there's no mid scoop / not much treble boost, there's not enough treble from the instrument for power amp harmonics to 'mingle in' with, causing them to stand out rather.
    Putting in a 6G3 vol/tone mixer arrangement seems to help with this, and also as the 2nd stage may be exhibiting blocking distortion as stock .
    Also the VB+ can be near 400V with some transformers / rectifiers, which can be good for a hard edged rock tone, but ~350-360V can sound sweeter.
    Pete.
    Last edited by pdf64; 01-07-2012, 05:33 PM. Reason: typo
    My band:- http://www.youtube.com/user/RedwingBand

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    • #3
      I used 470k, but I can go higher.

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      • #4
        Have you tried the Normal/Mic Channel at very overdriven settings? Should be rich & creamy.

        A 5V4 might help it hold together a bit longer before going ragged (if uncorrected plate voltage exceeds ~385vdc consider a 300-330ohm cathode resistor too) but "ragged" & "unpleasant" don't sound typical of a properly working 5E3. If it sounds like the amp is malfunctioning...then it probably is. Though as you point out, it's got little in common with a DRRI.

        Can you post pics of the circuit? These amps can be sensitive to layout & wire routings...even if voltages & components are OK.

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        • #5
          Getting the goods from a 5E3 circuit is all about player technique. For one thing, you've got to ride the guitar volume control; you're always making adjustments with it. Another is picking dynamics. Players that are not accustomed to tweed style amps have problems with this, especially the guys that always crank the guitar volume all the way up and never adjust it, that is a recipe for farty, blatty, distorted tone; and doubly so when using humbucker pickups. 5E3's played well can be one of the sweetest tones ever, and like a Telecaster, there are so many different tones available by varying the controls and playing techniques.

          With that said, I too like to cut some of the bottom end using some smaller coupling caps and a 4.7uf cathode bypass cap. But I have played many stock 5E3's and have no problems getting great, great tones from them. Again, it's all in the player's hands. He needs to develop his technique. Keeping in mind he'll never have a lot of headroom out of that circuit. If that's what he's wanting, it's the wrong amp.

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          • #6
            MWJB,

            Again, I'm not really a guitar player, so I'm not that articulate when it comes to discussing the different flavors of overdrive. I'm not sure I'd be able to identify "rich & creamy" overdrive if I heard it. I play enough to determine if an amp is working properly or not. This is really the first time I've worked on a DIY amp built and sold by an amateur amp builder, and it looks like it was reasonably well-done to me. I fixed a few iffy solder joints, but nothing major.

            This amp produces a clean sine wave on a scope that calculates to 14W, which should be about right. Cathode voltage is +22V with a 270 Ohm cathode resistor, and cathode-to-plate voltage is 360V. Tubes are NOS Sylvania 6V6GT, GE 12AY7 input tube, JJ ECC83 gain stage & PI, and CBS Hytron 5Y3WGTA. The current owner is a talented, but younger guitar player, and, in the end, I'm not entirely sure that this is the amp he really wants.

            I did install a 1 Meg grid stopper on the PI, and that seems to help. As you requested, I'm attaching a pic of the build.

            Click image for larger version

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            • #7
              Originally posted by pdf64 View Post
              How big did you do with the grid stopper? 1M is fine, won't cut treble (due to there being no voltage gain) and may help to smooth it out.
              I went up to a 1M grid-stopper, and that did, in fact, smooth it out. I appreciate the help!

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              • #8
                Try bumping up the grid stoppers on the 6V6's, as high as 100K and see if that helps.

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                • #9
                  I think you have an extra "0" in there? ;-)

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                  • #10
                    Nope, I meant one-hundred-K. Refer to the "Avoiding unpleasant overdrive tones" paragraph here:

                    The Valve Wizard

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                    • #11
                      Needing 100K grid stoppers on a 5E3...or anyother Fender based design is a sure sign that you have bigger issues elsewhere.

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                      • #12
                        Originally posted by Rhodesplyr View Post
                        MWJB, ...
                        This amp produces a clean sine wave on a scope that calculates to 14W, which should be about right. Cathode voltage is +22V with a 270 Ohm cathode resistor, and cathode-to-plate voltage is 360V. Tubes are NOS Sylvania 6V6GT, GE 12AY7 input tube, JJ ECC83 gain stage & PI, and CBS Hytron 5Y3WGTA. The current owner is a talented, but younger guitar player, and, in the end, I'm not entirely sure that this is the amp he really wants.

                        I did install a 1 Meg grid stopper on the PI, and that seems to help. As you requested, I'm attaching a pic of the build.

                        [ATTACH=CONFIG]16737[/ATTACH]
                        It looks good to me too. I think it is a kit from Ceritone ... looks like one of their painted or powder coated chassis. I don't know what they use for output transformers but a cheap one can make a difference too.
                        360v plate to cathode is a little high for classic 5E3 tone but still OK.
                        14 watts output is high too... was that measured into a speaker or a dummy load and at what frequency?
                        After many many hundreds and hundreds of these amps... I also run into players who simply just cannot squeeze "the tone" out of a tweed amp! ha ha. You might have to reconsider it and suggest something else.
                        Bruce

                        Mission Amps
                        Denver, CO. 80022
                        www.missionamps.com
                        303-955-2412

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                        • #13
                          All problems were solved with the 1 Meg grid stopper on the phase inverter. Both the sound and the trace on the scope testify to the improvement.

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                          • #14
                            OK cool.. I would say that you should never need a 1M grid stopper resistor on the 5e3 PI so.... I don't know what the actual problem was and probably still is.
                            Regardless, I live by this rule:
                            #1 What ever sounds good, is good.
                            Bruce

                            Mission Amps
                            Denver, CO. 80022
                            www.missionamps.com
                            303-955-2412

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                            • #15
                              In Rhodesplyr's other 5E3 thread, a speaker change is detailed. The original speaker was a vintage PA type with a wizzer cone; that may have been responsible for some harsh/unpleasant overdriven tones.
                              My band:- http://www.youtube.com/user/RedwingBand

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