Help Me Tame This Crazy Reverb Please

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by hardys, Apr 9, 2015.

  1. hardys

    hardys Member

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    I recently bought a used Vibrolux clone and while I love the amps overall sound, the reverb is killing me. It's very touchy trying to dial in a little to medium verb, because once you get to 3 it takes a big jump into some seriously surfy territory. On 5, it sounds like the usual Blackface verb on 10. Past 5 and it just gets WAY over the top and at 10 it's just ridiculous and totally unusable.

    FYI...The tank is a 17", 3 spring Accutronics.

    I've read a few threads on the web saying that substituting a 12AU7 for the 12AT7 in V3 can help tone the verb down and give the pot a more gradual taper. Before I drop $25.00 or more on a NOS 12AU7, I wanted to check in here and see if this is a viable solution.

    Whatcha think, techies? Will this work?

    Thanks for any help in advance!!! :beer
     
    Last edited: Apr 9, 2015
  2. swiveltung

    swiveltung Member

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    Fender reverbs are famous for being off at 2 and sound full on at 3.5. There is a mod you can do to replace the pot with a lower value and add a resistor... ( I think I've got that right) This gives you the reverb range that is normally 0-5 but spreads it over 0-10 giving you more control.
    You can try the 12AU7 first.
     
  3. hardys

    hardys Member

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    I just found a thread here from 2011 suggesting using a 12dw7 in V4. It claims one side is comparable to a 12UA7 which will tame the verb and the other side is comparable to a a 12AX7, which will pass the signal along at the proper level. Thoughts on this please?
     
  4. EFK

    EFK Supporting Member

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    Most Fenders use a 100K *linear" reverb pot. Probably the best thing you can do right off the bat is change that out to a 100K audio pot. Also the 12AU7 swap is very common, very easy and just about as cheap as the pot swap. Either - or both in combination - ought to rectify the situation.
     
  5. Silent Sound

    Silent Sound Member

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    The original Vibrolux reverb just had a 2 spring tank, so that may be something to consider. Especially since they're about $30 new and something a monkey could install (with the proper training). That would effect the sound of the reverb as well. Personally, I'm prefer the long 2 spring variety.

    There's also the dwell mod you could consider. That would be a bit like throwing a lower gain tube in there. It would affect the amount of signal being fed into the reverb tank, and the normal reverb control effects the amount of signal coming out of the reverb tank.

    As for the 12DW7, it may work. You could try it and find out, but I doubt it would be what you're looking for. The reverb driver uses both sides of the reverb tube in parallel, so that kind of defeats the purpose of having two different triodes in a single tube. I'd rather go with a 12au7 or 12AT7 in that slot. You can probably find some ANOS 12AU7's for pretty cheap. They're pretty common and much less desirable than 12AX7's.
     
  6. Tone Meister

    Tone Meister Member

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    One half of V4 is for reverb recovery and the other half of V4 is the second gain stage for the Vibrato channel. The 12DW7 is one half 12AX7 and one half 12Au7 and will work as will any of the other changes suggested above. If you decide to use a 12AU7 it should go in V3, the reverb driver. I would take a look at the tank also to see which one you have. That alone can make a big difference.

    This REVERB TANK INFORMATION should answer most any questions you may have about the tank itself.
     
  7. pdf64

    pdf64 Member

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    True but both sections of V4 share a cathode resistor and 12AU7 tend to pass more current than 12AX7, so the bias voltage of the 12AX7 stage is increased, resulting in it running cooler / lower gain etc.

    The best way forward may be the 100k audio taper pot for the reverb intensity control, however additionally I replace the V3 1M grid leak resistor with a 470k + 470k potential divider.
    This reduces the tendency of V3 to overdrive a little, and acts to isolate the dry signal path from clipping when it does happen. It sounds horrid though it's generally not discernible through all the power amp overdrive.
     

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