66 Bandmaster Ohms?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by T-bone, Sep 20, 2004.

  1. T-bone

    T-bone Member

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    Hi
    Just got a 66 Bandmaster Head and the previous owner told me it was a 16 ohm speaker out But I did some research and Blackface Bandmasters between 1963-67 have a 4 ohm out?

    Got my info off http://www.ampwares.com/ffg/index.html


    What gives?

    and oh yeah. I had to try it out in my 16 ohm cab and it sounded just fine

    Thanks
    Steve
     
  2. Wakarusa

    Wakarusa Member

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    IF it still has the stock output transformer 4 ohms is the correct impedence. Running into a 16 ohm load is asking for trouble.

    If the OT is non-stock, who knows.
     
  3. T-bone

    T-bone Member

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    Bummer. All I have is a 16 ohm cab.

    Is there any way to measure the ohms coming out of the amp?
     
  4. Wakarusa

    Wakarusa Member

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    Well, sorta. There are definitely ways to figure out the turns ratio of the output transformer, but I'd guess that it's a bit more than you might want to get into.

    First test should be to see if the output transformer appears stock. You can get an idea by reading the numbers off of the end bell for manufacturer, date, and model. You can post 'em here if you don't know what to look for.

    Also, what kind of cab is it? You might be able to re-wire it for 4 ohms.
     
  5. T-bone

    T-bone Member

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    I've got-

    CSA (Not sure about this one hard to read)
    25P 70
    606-537


    Thanks
     
  6. T-bone

    T-bone Member

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    My Cab is a 1x12 so options are limited.
    I use another amp with this cab and its 8 or 16 so I may need a new cab if the head is a 4 ohmer.
     
  7. Wakarusa

    Wakarusa Member

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    Sure looks like the stock OT from here. 4 ohms is the recommended load.

    As you've already discovered it will work into the 16 ohm load. The question is for how long. For the gory details search on the term "flyback".

    Sorry :(
     
  8. T-bone

    T-bone Member

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  9. Wakarusa

    Wakarusa Member

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    I've been wondering how well Ted's matching transformers worked out. If you score one please post a review.
     
  10. renico00

    renico00 Member

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    I agree, that's probably the original at 4&#8486.

    Jeff
     
  11. T-bone

    T-bone Member

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    Just ordered one. Seems like a great idea. Will let ya know what I think.
    Thanks again for the help.
     
  12. jdtele56

    jdtele56 Member

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    Most early Fender heads are 4 ohm loads running 16 ohm cab is fine. The rule is: larger is cool lowere is not.
    A 16 ohm cab might not be as load than a 4 ohm but not by much. You can't go under 4 ohms. A 2 ohm laod could fry the transformer if a tube shorted out etc.
    Early Fender piggyback rigs were 4 ohm heads with the cab having 2 8ohm speakers wired in parelell which equals the match load of 4 ohms.
    Te early Fender heads main & extension speakers were not wired in paralell. Eack jack has the same ohms rating off of the transformer.

    Hope this helps

    Denny
     
  13. Wakarusa

    Wakarusa Member

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    Correct for a solid sate amp, exactly backwards for a tube amp.

    A tube amp rated at 4 ohms output driving a 16 ohm cab is begging for trouble.
     
  14. drbob1

    drbob1 Silver Supporting Member

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    Perhaps we need to be a bit clearer about why. When the speaker returns to the neutral position twice each cycle, the voice coil moving thru the magnetic field produces a voltage opposite to the one that pushed the voice coil to start with. This "back EMF" goes thru the output transformer backwards and appears as a voltage surge to the tubes. If this surge is too high, it's likely that the circuit will arc-causing voltage to flow where it's not supposed to and burning components, which can in turn destroy the OT. For Fenders the general rule is no more than a factor of 2 mismatch...
     
  15. countandduke

    countandduke Member

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    I too just picked up a Bandmaster and I have a 16 ohm cabinet that it sounded good through. What differences can I expect if I were to use an 8 ohm or even a 4 ohm speaker cabinet?? Is there a large volume increase when going from 16 ohms to 4 ohms when the amp is putting out 4 ohms???

    Chris
     

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