Ampeg V4BH Question

Discussion in 'Amps [BG]' started by Rock-N-Dawg, Jan 22, 2014.


  1. Rock-N-Dawg

    Rock-N-Dawg Supporting Member

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    I know this is probably covered already on the forum somewhere, but i can't seem to find it. I bought a used Ampeg V4BH (not sure if it's the older or newer version it has the red and blue lettering!) Anyway i really dig the way it sounds and as is it's probably loud enough for my current band (plus it looks cool sitting on my 106HLF). But after reading the tons of forum posts I was thinking of trying a couple 5751, EC803S or 12AY7 preamp tubes to try and mellow the gain down a little (currently it starts getting out of control headroom wise at only 10 o'clock.) Reading the posts there is a lot of great info, and suggestions but nobody really says if the preamp tube switch actually helped any or did anything. Also the main reason I'm writing this is I can't find a schematic/tube layout diagram i can buy or download which shows which tubes are which. Being some of the post talk about switching out the V1 tube, I have no clue where V1 is? Are the preamp tubes the ones you can see from the back or the internal ones? And which one is the V1 I want to try switching out. Any help with this would be appreciated.
    PS Seems strange to me that the tube layout doesn't show up in the cabinet or even worse in the manual! thanks ed
     
  2. JimmyM

    JimmyM Supporting Member

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    Honestly, all I think that replacing pre tubes with lower gain tubes is move the breakup point a little higher on the dial. Yours is typical of Ampeg tube amps, giving it up to breakup right around the 10-11:00 mark when the master is cranked up all the way. Instead of throwing money at tubes, I'd just back off the master a bit. You will start getting preamp compression past the normal breakup point, which may or may not be desirable, but you will have more room on the dial.
     
  3. beans-on-toast

    beans-on-toast Supporting Member

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    Ed, I agree that it is odd that they didn't include a tube layout diagram. V1 in the pre-amp is closest to the input jacks. Try a 12AY7 (6072A is a low noise version, even better) in the pre-amp V1 and see if you prefer it.

    A tech should see if the power tube bias setting is optimal. This can clean the amp up a bit. If your power supply caps need to be changed, you could be suffering from a lack of headroom and early distortion.

    It is also possible to buy a matched set of power tubes that have a later onset of distortion. A good tube seller (such as tctubes.com) can help you with that. Depending on the tubes that you have in there now, this could make a difference.

    Hope that the image below helps.


    David



    [​IMG]
     
  4. Rock-N-Dawg

    Rock-N-Dawg Supporting Member

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    Wow thanks David!
    That's even cooler than a schematic!
    I haven't broke into mine, the guy said he replaced all the tubes right before I bought and claims the bias was set.
    As stated i will probably try the 12AY7 or maybe a 5751 being I don't want to change the way it sounds. Being the V2 is a 2AU7 I take it i should only switch out the V1 ( I actually thought both the preamp tubes would have been 12AX7s?)
    Jimmy thanks for the comments, mostly from an Ampeg expert like yourself...I'm kind of thinking the same thing and it's just the nature of the beast....But i figured preamp tubes are cheap and might as while see what it does. I haven't tried it with the band yet, but Im in a not all that loud Rockabilly band so it should be more than OK as is.
    I'm so used to carrying my little 1-12 Markbass stuff around it might be hard to actually talk myself into dragging 150 pounds of stuff out of the bedroom anyway....it does sound cool though!
     
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  6. Rock-N-Dawg

    Rock-N-Dawg Supporting Member

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    Took my amp a part, it had a 12AX7 in both V1 and V2 (should have been a 12AU7 in V2). Just ordered a new JJ 12AU7 for V2 and a JJ 5751 for V1 to try first, I will try the 6072A next. Thanks again.
     
  7. B-string

    B-string Supporting Member

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    V2 being a 12AX7 was wrong, that is a higher gain but lower current tube. The 12AU7 is most likely being used in a cathode follower for the tone circuits. You might get a whole new appreciation for the unit after V2 is replaced.
     
  8. beans-on-toast

    beans-on-toast Supporting Member

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    Did the power amp have the correct tubes?
     
  9. Rock-N-Dawg

    Rock-N-Dawg Supporting Member

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    It has a set of russian sovtek 6L6WXT+ tubes, hopefully those are right..they look new (the preamp tubes didn't!)
     
  10. beans-on-toast

    beans-on-toast Supporting Member

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    I'm confused. When you said V1 and V2, did you mean the pre-amp or the power amp?

    I was asking about the small signal tubes in the power amp. The ones in J12 and J13. Having a 12AX7 in J13, the one that drives the power tubes, could be a problem. A 12AX7 in V2 in the preamp could be more noticeable if you are connecting a DI or something else to the pre-amp out. In this case the 12AU7 would provide more drive to split the signal and handle both the pre-out and the power amp. How well a 12AX7 in V2 will do depends on what you are connecting to the pre-out. It may not be an issue.
     
  11. vistacruiser

    vistacruiser

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  12. JimmyM

    JimmyM Supporting Member

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    Well maybe replacing v2 with the correct tube will get the desired results. Worth a shot.
     
  13. Rock-N-Dawg

    Rock-N-Dawg Supporting Member

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    The J13 and J12 seem to be correct (j13 = 12au7, j12 12ax7).
    Im going to change the V2 to the correct 12AU7 and the V1 to a slight lower gain 5751. As stated even if this does nothing, I still really dig the way this thing sounds, and I'm sure it will actually be more than loud enough as is anyway. I was always running the master max, so I will also goof around with lower master and higher gain settings as Jimmy suggested.
    Thanks everyone for the help and the fast response!
     
  14. beans-on-toast

    beans-on-toast Supporting Member

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    OK, so far so good. When you get your new 12AU7 and 12AX7 tubes, I would try them in the power amp as well just in case the ones that are there now are weak.


    BTW, the pre-amp in the V4BH is the same as the one in the SVT CL. The voltages are the same as well. They use a 12AX7 in V1 and V2 in the CL.
     

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