higher headroom 12ax7's....

Discussion in 'Amps and Cabs' started by tlester, Oct 26, 2005.


  1. tlester

    tlester Member

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    Hi Guys -

    I have a Black Cat amp, with two channels. The are both "full" channels.... i.e. one isn't really considered a clean vs. dirty. The A channel does seem to be a bit more clean and the B channel gets edgy quicker.

    Here's my problem.. I'm trying to run an ABY in front of it with A channel as clean, and B channel as dirty. However, I'm having a hard time keeping the A channel clean while getting it loud enough to be an acceptable volume difference when I jump to the B (dirty) channel. I end up with the B channel too loud or the A channel too dirty.

    The A Channel is currently running a pair of Ruby 12ax7's. I'm guessing they are stock, everything else has been replaced (and upgraded). Is there any 12ax7's that will have more clean headroom that I could replace the Ruby's with to get closer to a matched channel switch?

    Thoughts?

    -Tom
     
  2. fyler

    fyler Member

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    you could use a 5751, or a 12AT7.
     
  3. tlester

    tlester Member

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    I'm a tube novice... are those interchangeable?

    -Tom
     
  4. Chiba

    Chiba Gold Supporting Member

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    Yes - it sounds like you need to drop the gain in your A side's preamp by going to a lower-gain tube like a 12AT7. It's certainly worth a shot and won't harm your amp.

    --chiba
     
  5. AL30

    AL30 Member

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  6. jlagrassa

    jlagrassa Supporting Member

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    When I am looking for clean headroom I usually put in a 12AY7 which is very low gain compared to a 12AT7 or 5751.
     
  7. fr8_trane

    fr8_trane Member

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    I use a 5751 in the reverb channel of my modded Deluxe Reverb. It definitely increased headroom.
     
  8. tlester

    tlester Member

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    Hey... on this page, it makes this comment: "This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but...."

    My current problem is that I can't get the A channel loud enough while still remaining clean. Is the less gain-y tubes also going to be quieter? I.e. am I going to end up with the same deal? Just with the knob further clockwise?

    -Tom
     
  9. fr8_trane

    fr8_trane Member

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    A 5751 will reduce the gain in the preamp and only slightly reduce the overall volume which you can then make up by turning up the amp. In my case the amp stays cleaner at louder volumes than before because in many cases the preamp section will overdrive before the power amp especially if you're using humbuckers. The preamp is the limiting factor in this case.
     
  10. Reeek

    Reeek Member

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    Tube Gain

    12AX7 = 100

    5751 = 70

    12AT7 = 60

    12AZ7 = 60

    6072/12AY7 = 44

    5965/12AV7 = 27

    12AU7/6189/5814 = 20
     
  11. Blue Strat

    Blue Strat Member

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    Note that there are special considerations besides the gain of a tube. Some of these, like 12AT7s, require different circuits than 12AX7s and do not behave as specified when plugged into a circuit designed for another tube.

    IOW, when you plug a 12AT7 into a 12AX7 circuit, you can actually get less headroom and vice versa.

    Use your ears for your final decision, the numbers are only a rough guide.
     
  12. fr8_trane

    fr8_trane Member

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    This was my understanding of the 12at7 as well. However I thought (and correct me if I am wrong) that the 5751's are identical to 12ax7's in form AND function and therefore made the best sub for lower gain applications. It certainly provided my deluxe with more headroom as advertized.
     
  13. outtahear

    outtahear Supporting Member

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    Pair of AT7s cheap on the "pedals and everything else" Buy and Sell, if you wanna give it a shot..;)
     
  14. Guinness Lad

    Guinness Lad Silver Supporting Member

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    If channel A and B are on parallel circuits i.e. using different preamp tubes for each gain stage rather then using them in series. Read what I said twice, now! You could reduce the overall volume of the B channel instead of trying to increase the volume of the A channel (while keeping it clean). If channel B has more then enough dirt for you, use a lower gain tube. This will reduce the overall distortion some but it should also reduce the volume of channel B. I'm soory but I don't know anything about Bad Cat amps so I couldn't tell you how the preamp tubes function.

    I had to mess with my Guytron a bit to get the A and B channels eq'd close enough so the master tone controls would not have to be moved when switching from one channel to the other. Luckily for me the Guytrons preamp tubes are run as two separate circuits which feed into the power section.
     

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