Amps, Heads, Ohms, Watts, etc etc

Discussion in 'Amps and Cabs' started by caxelrod, Feb 15, 2012.

  1. caxelrod

    caxelrod Member

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    Ok... so, here's the deal. Ive never head a tube head/cab setup (always had a solid state or tube combo where I didn't need tow orry much about this), but can someone please educate me on the watts, ohms, etc?

    I have a Sovtek 60 watt head... that outputs at 4, 8, and 16 ohms.

    And a Marshall 1936 2x12 cabinet.

    Is the Sovtek 60 watts at 8 ohms? 4 ohms?

    Which impedance should I be selecting on the head? Which on the cabinet?

    Will these selections affect wattage output if I want to keep levels lower?

    Help! I'm not the "brightest tube in the head" when it comes to this...

    and the lack of any info on Sovtek amps makes a simple google search difficult.

    Thanks in advance.
     
  2. vibrostrat43

    vibrostrat43 Supporting Member

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    It's 60 at both as long as you have the corresponding tap connected to the correct speaker impedance.

    You'll only run at less power if you mismatch the speaker impedance to the OT tap's impedance.

    What ohm rating are the speakers? If they're 8 ohms the cab is either 4 or 16 ohms if both are on, but if they're both 16 ohms then the cab is 8 ohms if both speakers are running (I'm mentioning both speakers running because some cabs have stereo ins, or run one speaker (or speaker pair) with one tap and another with the other tap.

    Some people think the amp sounds better using the entire OT winding with 16 ohm tap and a 16 ohm load, but some prefer the other two with the correct corresponding load so it really all depends.

    PS: as a side note, and I'm not sure on this amp and it's hard to check (I don't even know how), but I know some marshall-type OT's are designed for relatively low primary impedances, and running twice the speaker impedance that a certain OT tap wants to see will double the primary impedance as well. Ex: Some OT have a 3.6k primary, and running the 16 ohm tap with a 32 ohm load (two 16 ohm speakers in series) will yield a 7.2k primary which is close to the primary that 6v6's like to see, and 6l6's sound their best to many ears at 6.6k which is not far off. This is really only desired when running tubes like 6l6's, 6v6's, or kt66's...el34's and 6550's prefer the stock primary impedance.
     
    Last edited: Feb 15, 2012
  3. caxelrod

    caxelrod Member

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    Thanks for the response, but it is far too advanced for me.

    The back of the cab says 16 ohms stereo, 8 ohms mono.

    So, I'm obviously selecting the 8 ohms mono... so, if I'm connect the amp at 8 ohms to the cab at 8 ohms mono, how many max watts is going out? 60? 30 per speaker? Is that how I should hook it up?
     
  4. vibrostrat43

    vibrostrat43 Supporting Member

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    Yes, the amp is putting out 60 watts, 30 per speaker when you plug the 8ohm amp tap into the 8 ohm cabinet tap.
     
  5. caxelrod

    caxelrod Member

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    Ok... thanks... now, I am just curious, if I selected 16 or 4 ohms from the head into the 8 ohm mono jack on the cab, what would that mean?
     
  6. wyatt

    wyatt Member

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    It's not advised.

    The speaker load can't change...it's fixed... and the output transformer/windings ratio can't change..it's fixed as well...that means the power tubes have to absorb the change in primary impedance, resorting in a change in tone, a compromise in performance, and a string on everything in a rather hot power amp.

    It short, the amp doesn't work as well. Most gig worthy amps are built to handle the abuse and keep on chugging, but they won't run at their optimum. Vintage amps with old output transformers, amps with small output transformers, amps with cheap output transformers, etc. may not absorb the abuse and damage may result.

    Tube amps are NOT solid-state stereos, where the output is halved or doubled as you change the impedance.
     

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