PPIMV - Does It Drop Wattage?

Discussion in 'The Workbench' started by pedecamp, Oct 24, 2021.

  1. pedecamp

    pedecamp Well-Known Member

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    When I use the ppimv in my 1959 is it actually dropping the wattage along with the volume? The reason I ask is I have some 75 watt creambacks and I wanted to do some sound testing without damaging anything. I have a 65 and 75 creamback paired up in a 2x12 and I wanted to hear what each sounded like individually with the amp. I did try it at low volume for just a moment but I wanted to do a little longer and louder to determine which speaker I like better.
     
  2. Pete Farrington

    Pete Farrington Well-Known Member

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    Kinda, but then any volume control does. Can’t regard them as output wattage regulators, eg setting to halfway doesn’t equate to halving the output wattage.

    Use a resistive load of the same resistance as the nominal impedance of the speaker in question. Get the sound you want and turn up the master until you measure the VAC that equates to eg 50W on the resistive load. Then swap to the speaker without adjusting the settings.
    Power = V squared / R
    So 20VAC across 8ohms equates to 50W.
     
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  3. pedecamp

    pedecamp Well-Known Member

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    Sorry Pete too technical for my understanding but I appreciate it. Can I do what I want for my speaker test without risking damage to the amp or speaker?
     
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  4. Pete Farrington

    Pete Farrington Well-Known Member

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    If you keep the signal totally clean, then the risk is low. But with a 1959, that pretty much rules out the bright channel.
    Overdriven, without the precaution I noted above, all bets are off.

    Are you able to monitor the HT voltage or output valve current whilst playing? eg with a bias probe.
     
    Last edited: Oct 24, 2021
  5. pedecamp

    pedecamp Well-Known Member

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    So having the ppimv engaged is no help? How I have the amp set is bright channel on 5 and ppimv set to tv volume.
     
  6. Pete Farrington

    Pete Farrington Well-Known Member

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    You’d need to play loud enough to be flapping your flares and shaking things off the shelves before those speakers are going to start feeling it :jam:
     
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  7. pedecamp

    pedecamp Well-Known Member

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    Nah that wont happen, Im a basement/backyard player! Maybe I'll just pull a pair of power tubes for a safe speaker test if thats what I gotta do.
     
  8. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    Here’s the deal, the PPIMV “should” lower the wattage output of the amp. The reason it’s there is to reduce the output section power/volume and to allow preamp distortion. If you are conservative with the output volume, you should be fine but you have to be realistic about it. A 100 watt amp can damage the speakers.
     
  9. Pete Farrington

    Pete Farrington Well-Known Member

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    Unless you’re playing loud enough to seriously annoy someone at the other end of your house, overpowering a 65W Celestion ain’t going to be an issue.

    A typical 1959 running of 2xEL34 will put out 60W clean, cranked 100W.
     

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