Amp Technical Question?.

Discussion in 'Amps and Cabs' started by bluesjunior, Sep 5, 2008.

  1. bluesjunior

    bluesjunior Member

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    I was reading the two threads here yesterday on pulling tubes from the amp for less power.

    I have a Carlsbro 60 Twin amp head which I run through a closed back 2X12 cab rated at 8ohms. The amp has the following installed.

    Tubes: 4 12ax7 & 2 EL34
    - Channel 1: 2 inputs - treble - bass - volume
    - Channel 2: 2 inputs - treble - bass - response - volume
    - For both channels: limiter - presence - reverb
    - Voltage selector
    - Impedance selector

    I play mostly at home and this is a very loud amp for that situation but I have recently started using it again as I can get a great sound out of it with my 25db midboosted Strat which can easily overdrive it at low volumes.
    I have the guitar plugged into the low impedence socket and the Bass & Treble around 12 o'clock, The volume knob goes from 0 - 5 and I have it set aroundabout 1/2 to 2/3rds from 0 - 1 any louder and it starts pictures on the walls vibrating etc. After reading the other threads yesterday I wondered if it was possible to pull one of the EL34's and alter the ohm selector switch from it's present 8ohms to 4ohms. I would just like to be able to let the amp do a little more work without getting any louder if you understand me.[​IMG]
     
  2. dwoovre

    dwoovre Member

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    In a push-pull amp, (which I assume yours is, based on 60W out of 2xEL34), the output tubes work in pairs. Pulling one will only amplify about half of your signal, and may damage your amp. The method of pulling tubes only works in a push-pull amp when you have a 4-tube output section, and you can pull one pair.
    You might want to look into an attenuator.
     
  3. Blue Strat

    Blue Strat Member

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    +1. Unless it's a single ended amp with 2 or more power tubes (very rare), this won't work. You need at least 4 power tubes.

    Note that this should not be done on "cathode biased" amps that share cathode bias resistors. Examples are AC30s, DC30s, SC30s, and many other 4-EL84 amps. You'll destroy the remaining power tubes.

    If you're not sure what you have, check with the manufacturer before pulling tubes.
     
  4. bluesjunior

    bluesjunior Member

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    Thanks for the replies guys I will just leave well enough alone then.:jo
     
  5. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    I you want to tame your amp down a bit, a safe thing you can do is run a 12AU7 in position 1 or 2 in your pre amp. This tube is compatible but has much less gain than the 12AX7.

    If the 12AU7 trims the volume too much, you can try a 12AT7 which is somewhere between the 12AU7 and the 12AX7. Too, you can experiment and maybe run a pair of 12AT7s in V1 and V2.

    This will decrease the overall volume of the amp, but the cool thing is, you'll have more headroom and you'll work your power tubes a little harder to get a good crunch. You may end up wanting to experiment with pedals to get some serious overdrive going.

    Too, you can jsut get a hotplate and not worry about the amp. :)
     
  6. Blue Strat

    Blue Strat Member

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    Here we go again....

    Using lower gain preamp tubes doesn't work your power tubes harder, it has the completely opposite effect.

    The only way to work your power tubes harder is to play LOUD or dime an amp into an attenuator. This includes using the highest gain preamp tubes possible.

    Can we have a sticky on this one? This misconception is repeated over and over and over.....
     
  7. SatelliteAmps

    SatelliteAmps Member

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    If we got rid of all the misconceptions, this would be a very lonely board.
     

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