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1967 Bassman Extension Cabinet Question

Discussion in 'Amps and Cabs [BG]' started by bmk, May 17, 2007.


  1. bmk

    bmk

    Jan 28, 2007
    Hi guys- Maybe you can help me with this question. I have a 1967 Bassman with the smaller 2X12 stock cabinet. Can I connect an identical 2X12 stock cabinet (with the same ohm rating) into the extension speaker jack without damaging the amp? Thanks in advance for any help on this matter!
     
  2. If your amp is a '67 tube Bassman, you can certainly use two cabs without problems as the load is less critical for tube amps.

    The Fender Amp Field Guide has a lot of info on Fender amps through the ages. Try the link below:

    http://www.ampwares.com/ffg/
     
  3. pocket_groover

    pocket_groover Supporting Member

    Jan 21, 2004
    Northern California
    I got a '65 bassman 2x12 when it was new. Played it with an extension 2x12 many times and never had a problem. Tube amps are a little more forgiving on low impedance loads than solid state. It's the open circuit (no speaker situation) that will fry the tube amp (the output transformer makes mondo voltage and will either short out or arc the tube sockets).

    In fact, the head by itself is capable of blowing out the single 2x12 bottom speakers (I've done that too), so it's plenty good for an additional cab.
     
  4. bmk

    bmk

    Jan 28, 2007
    :bassist: Thanks for the input!! I will get back to you and let you know how it sounds.
     
  5. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    To be sure:
    Have you double checked the ohm loads on these two cabs?
    (unless you bought them new, someone else could have replaced speakers
    or rewired them to a much different load than original)

    Also what info does your amps, speaker output labeling give?
     
  6. pocket_groover

    pocket_groover Supporting Member

    Jan 21, 2004
    Northern California
    Anderbass does have a good point; check the impedances before you try it. The original cab was two 8 ohm speakers in parallel, so a 4 ohm load. With the extension, it became a 2 ohm load. The head is still happy with this; Fender used to sell identical amp bottoms for use as extension speakers.

    However, as anderbass has pointed out, someone could have modified the cabs for 2 ohms each, in which case you'd be dealing with a 1 ohm load!
     
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The Bassman was specifically designed to use a second cab and you won't have a problem with it. OTOH, if you still have the original drivers in there you should seriously consider replacing them, as they have extremely limited bass capabilities. This driver, while not specified for electric bass, has very good specs for small sealed cabs, and would significantly outperform the original drivers.
    http://www.eminence.com/pdf/acoustinator-n2012.pdf
     
  8. Stick a patch or speaker cable in the jack.. put a multimeter on it, measure the impedence.. make a label for that cab. Do the same process for the other cab as well. That way nothing can get past your notice from that point forward. And if all else fails, do some internal investigation of the drivers/wiring topology.
     
  9. bmk

    bmk

    Jan 28, 2007
    Good Idea! I always wondered if that would work, but I've never tried it. I can save myself the trouble of opening up the cabinets.:hyper: Thanks for your time and input!
     
  10. <Originally Posted by Rattman>
    "Stick a patch or speaker cable in the jack.. put a multimeter on it, measure the impedence.. make a label for that cab. Do the same process for the other cab as well. That way nothing can get past your notice from that point forward. And if all else fails, do some internal investigation of the drivers/wiring topology"

    You are quite welcome to my humble advice. Its not that I don't trust anyone, its just that I don't trust anyone.. therefore I always do my own independant investigation of ANY piece of gear I aquire.. new or used, regardless of how it is 'marked'. I'll determine it's true output or impedence. And if the gear needs to be modified to meet a specific usage, I'll design a modification and then implement it.

    Lets us know how your idea turns out with your two cabs.
     
  11. AckAckAttack

    AckAckAttack

    Aug 27, 2006
    do they have regular multimeters with 1/4" jacks that could measure total impedence?
    I thought the only way was to open it up and connect one side to the negative and the other to the positive?
     
  12. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Maybe, but the method below works just fine with a regular multimeter.

     
  13. bmk

    bmk

    Jan 28, 2007
    :meh: After checking the impedance on both cabs, I hooked them both up to the bassman head. Other than a drop in the volume when the second cab was plugged in, I had a hard time telling the difference between a single or double cabinet. I'm not sure what I was expecting, but it wasn't anything earth shattering. The nice part about it is that it raises the head up to a level where I can adjust it without having to bend over (which, by the way, seems to get harder every year!). Thanks for all of your time and input, I really appreciate it!
     
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You'd notice a difference with the amp cranked. With two cabs it will go louder (6dB, to be exact) before farting out.
     
  15. pocket_groover

    pocket_groover Supporting Member

    Jan 21, 2004
    Northern California
    Hmmm....two cabs should be noticeably louder than one. I've done this many times. It could be that one cab is wired out of phase with the other? You can tell by putting a 9v battery across the tip and sleeve of the plug that would go to the amp while the other end of the cable is plugged into the speaker. When you do this, watch the cone with a flashlight to see if it goes in or out. Do the same with the other cab but make sure the polarity of the battery is the same as the time you did it with the first cab (+ to the tip and - to the sleeve for example). If the second cab cone goes in while the one in the first cab goes out, they're out of phase and hooking them up together will be softer. To fix this, reverse the connections on one side of one of the speaker cables.
     
  16. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    +1,
    Good tip there pocket groover.
     
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    True with SS amps, which have constant voltage output, and you get an instant 6dB increase. Not necessarily so with constant current tubes, where the 3dB increase may not be so obvious. But checking the cab phase isn't a bad idea.
     
  18. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    May 8, 2021

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