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Grid clipping or ?

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  • Grid clipping or ?

    Ok guys so here's an updated schem of this amp. I'm having trouble w/ the 2nd stage of the OD. I get 10v of signal out of the plate of V4 but the grid of V2 clips hard at 5v of signal with the gain cranked. I've tried up 13k on cathode of V2 w/ no change. Well the cathode voltage goes up to 4.5v w/ 13k but the clipping remains at that point. I thought that maybe the Ra of V4 was too low and the plate supply was clipping but obviously its not if the plate signal after the coupling cap is 10v. Can someone shed some light on what I'm missing here? I'd like for it not to clip that early on the grid of V2. FYI the negative portion of the signal is fine - no clipping. Oh and V4's plate is at 240vdc and V2's at 260vdc.
    Last edited by tboy; 11-18-2009, 10:33 PM. Reason: removed corrupt attachment

  • #2
    Hi Lowell. Can't open your attachment, can you re-post it?
    Some waveform pictures would help a lot.
    BTW, what's the +B voltage when you have those 240 and 260 plate volts?
    Juan Manuel Fahey

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    • #3
      here's the new schem. almost final, amp is sounding great. I would still however like your input on the initial post.

      power supply schem included too, however I've yet to implement the tube rectifier. as of now it's a ss rect, but everything w/ filters and dropping r's are correct.
      Attached Files

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      • #4
        are you speaking of r6 or r11 on v2? why is r6 33k? i know i know...question with a question.

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        • #5
          booj,
          33k on the cathode for a cold biased stage. it adds a really cool "fizzy" or "sizzle" quality to the OD channel.

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          • #6
            Hi lowell

            Couldn't open those attachments for some reason. My guess is you might want to try more attenuation and/or frequency shaping between the stages (e.g.; 22k/82k, 34k/68k, 47k/47k, 68k/34k, or 82k/22k split load plate resistor on the 1st stage, and/or voltage divider 470k/470k, 390k/390k, or even 470k/220k or 470k/100k? - possibly with the numerator bypassed by a 100pF to 500pF cap - to get the bass out and accentuate the mids more, lower coupling cap value - .01uF, 500pF?, grid stopper 10k-470k) or reduce the bypass cap on the first stage to 1uF or less - or try Marshallesque Rk/Ck values there (but can't see what you've got because I can't open the schematic) 2CW
            Building a better world (one tube amp at a time)

            "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

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            • #7
              Do you mean that the stage clipps at 5V input signal or at 5V signal at the otput of the same stage.
              At 5V input to the V2B it will clipp. And the only thing to do about it is to reduce the input signal.
              I dont see why though. This is a high gain OD Slo style. Thats what it does.

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              • #8
                'I get 10v of signal out of the plate of V4 but the grid of V2 clips hard at 5v of signal '
                I don't understand the query, have you got V4 and V2 mixed up in the OP?
                My band:- http://www.youtube.com/user/RedwingBand

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