Speaker ohm question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by atomheartmother, Jul 8, 2006.

  1. atomheartmother

    atomheartmother Senior Member

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    I have an old 60's Japanese head (looks like a blackface Fender) that I'm not sure of what the output impedance is. I remember seeing 4 ohms being printed on the output transformer. I talked to a tech and he said it'd work well with 8 ohms (something about there being stereo outputs or something, I don't remember).

    Anyway, assuming it is meant for 8 ohms, can I use it with a 16 ohm speaker? I wouldn't be cranking it if that matters (no higher than like 2 or 3).

    What if the output impedance is 4 ohms?
     
  2. atomheartmother

    atomheartmother Senior Member

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    Anyway to tell what the output impedance is?
     
  3. atomheartmother

    atomheartmother Senior Member

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    There's no original speaker; it's a head.

    Anyway, the bigger transformer (the power transformer, I assume) has 4 ohms (the horseshoe sign, actually) printed on it. The amp also has two speaker outputs (speaker and ext. speaker). For whatever reason, my tech figured it was 8 ohms because of the two speaker outs or something.
     
  4. donnyjaguar

    donnyjaguar Member

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    It can be determined by some experimentation. If you like I can re-post the process. If you're not comfortable working with high voltage I wouldn't recommend it.
     
  5. atomheartmother

    atomheartmother Senior Member

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    Thanks anyway. Maybe I'll have my tech check it out.

    BTW: What are vintage Fender heads usually rated at? Cosmetically this amp looks very similar to a BF Fender. The circuit is supposed to be similar to a Super Reverb as well. The tubes are different though (EL-34).
     
  6. cameron

    cameron Member

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    It depends entirely on what speaker cabinet a Fender head was originally sold with. Fender standardized on 8 Ohm speakers at some point quite early on, so amps were designed to want either 8 Ohm , 4 Ohm, or 2 Ohm loads, depending on whether they were sold with 1, 2 or 4 speakers, respectively. Thus a Bassman head, for example, wants a 4 Ohm load, as it was originally sold with a 2x12 cabinet.

    The Showman is a good case in point. The only difference between a BF Showman and a Dual Showman is that the latter was sold with a 2x15 cabinet. Thus the basic Showman wanted an 8 Ohm load, to match its 1x15 (or 1x12) cabinet, and the Dual Showman wanted a 4 Ohm load.
     

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