Impedance inqury

Discussion in 'Glowing Bottle Tube Amp Forum' started by KingFool1, Sep 20, 2020.

  1. KingFool1

    KingFool1 TDPRI Member

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    I have a Peavey Delta Blues 115 which runs 16 ohm speaker. The ext. speaker jack is also designed for 16 ohm cabinet. I only have a 110/8 ohm cabinet.

    My question is this. Can I add a resistor to make it act like a 16 ohm cabinet?

    I never run it at high volume so I'm not too worried about adding as is, but I realize it's not ideal. The transformers are never really being pushed.
     
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  2. MuddyWolf

    MuddyWolf Tele-Meister

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    Just use the 8 ohm cab. Most amps are designed to handle it except Marshall.

    Not my fault it it smokes though. At your own risk.
     
  3. Collin D Plonker

    Collin D Plonker Tele-Afflicted

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    I wouldn't try it, myself. I'd get a 16 ohm speaker to put in the cab.
     
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  4. D'tar

    D'tar Friend of Leo's

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    When two 16ohm speakers are plugged in... the switching jack, forget which one, check the schematic, then utilizes an 8 ohm tap on the OT. Plug a dummy load into the extension speaker and use you 8 ohm cab plugged into the other jack.

    Be sure to check the schematic to understand more clearly.
     
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  5. String Tree

    String Tree Doctor of Teleocity Ad Free Member

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    All kidding aside, download the PDF of the Owners Manual and read it.
    An 8 Ohm Load on a 16 Ohm circuit can lead to overheating of the components. Even at Low Volume.

    Take care.

    -ST
     
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  6. Wally

    Wally Telefied Ad Free Member

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    And so it is......
    https://el34world.com/charts/Schematics/files/Peavey/Peavey_deltablues.pdf
     
  7. Burning Fingers

    Burning Fingers TDPRI Member

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    The schematic shows that when you plug a cab into the external speaker that the internal speaker is disconnected from the 16 ohm tap on the output tranny and both the internal speaker and internal speaker are connected in parallel to the 8 ohm tap.
    You need a 16 ohm extension speaker to give a total of 8 ohms to match the 8 ohm tap.
    If you use an 8 ohm extension speaker the total load drops to 5.33 ohms.
    You may get away with it for a while but you may also end up looking for new power tubes and output transformer.
     
  8. schmee

    schmee Doctor of Teleocity Silver Supporter

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    I wonder if he could just use a Y cable then and be at 8 ohms?
     
  9. Wally

    Wally Telefied Ad Free Member

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    One could use a dummy plug in the extension spkr jack in order to tap/switch into that 8 ohm winding. Then, run the 8 ohm load out of the main speaker jack.
     
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  10. Burning Fingers

    Burning Fingers TDPRI Member

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    I may be mistaken but I thought the internal speaker was hardwired to the amp....the schematic shows it done that way...so one could not use a non existent internal speaker jack.
    You would need to disconnect the internal speaker at the speaker terminals and insulating the lead ends so no shorts can happen and then plug your 8 ohm cab into the extension speaker jack.
     
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  11. Wally

    Wally Telefied Ad Free Member

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    I stand corrected, Burn8ng Fingers. That would indeed complicate things.
     
  12. Paul G.

    Paul G. Friend of Leo's

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    "Lather, rinse, repeat". "Can I repeat first to save time?"
     
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  13. Burning Fingers

    Burning Fingers TDPRI Member

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    Yep I'm with you there Wally ..I find life is becoming more complicated the older I get...and there I was believing that it would get simpler.
     
  14. Bill Moore

    Bill Moore Tele-Afflicted Silver Supporter

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    I suppose a simple switch to open the internal speaker is out of the question?
    One would have to be aware though!
     
  15. printer2

    printer2 Poster Extraordinaire

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    It is doable without any modification and the dummy plug was needed, as said check the schematic (I'm feeling lazy).
     
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  16. D'tar

    D'tar Friend of Leo's

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    I just looked at my delta blues since its been a while... There is not a stock speaker jack but the terminals are not soldered. We were experimenting with 8 ohm speakers and the dummy plug as mentioned earlier.
     
  17. printer2

    printer2 Poster Extraordinaire

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    OK I looked. The internal speaker is hardwired but it run through a switch in the external speaker jack. J12 - J14 is the speaker, goes through the connector block to #1 of the external speaker jack, which then goes through a normally closed switch (opened when an external speaker is plugged in) to #2 of the jack to the 16 ohm winding. The schematic shows a tip connector (to engage the tip of the external speaker jack) is inline with the switched ring connector. This makes sense if you were going to plug in another 16 ohm speaker.

    I just remembered what the dummy plug was for. It was if you only wanted to run one set of output tubes. You removed a set of output tubes and replaced them with an old set with the cathode and plate pins removed. The connector puts the internal 16 ohm speaker on the 8 ohm winding and you run the amp as a 15 watt amp.
     
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