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1947 Kalamazoo KEA speaker?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Amstrat, Nov 26, 2020.

  1. Amstrat

    Amstrat TDPRI Member

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    I need some help with a new amp that is being delivered

    I believe it ha a “field coil”

    10” 8 ohm

    what would be a good speaker for this?

    Will there need to be mods?

    2003 years Zion Tele with Lindsey
    Fralin pick ups

    thank you kindly

    Larry
     
  2. schmee

    schmee Doctor of Teleocity

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    It can be a field coil, or just an OT mounted on the speaker. If a Field coil, then you may be able to just replace with a normal speaker removing the field coil also.

    You need to test the amp and decide what you want to change, then let us know in order to recommend a speaker.
    Want more head room?
    Warmer?
    Brighter?
    Louder?

    LATER: OK, I found the amp. Pretty cool! They say it's a field coil, but I'm not sure ,I need to find the schem, but it's likely you can use various speakers. A Emi GA SC 10 might be nice. But try it first!
     
    Last edited: Nov 26, 2020
  3. Amstrat

    Amstrat TDPRI Member

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    Thanks

    schematic
     

    Attached Files:

  4. NTC

    NTC Tele-Holic

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    Do you understand what a field coil speaker is? That field coil acts both as a magnet for the speaker and as an inductor coil, part of the power supply filter.
     
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  5. David Barnett

    David Barnett Doctor of Teleocity

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    OOh, a self-split output stage!
     
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  6. Amstrat

    Amstrat TDPRI Member

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    Actually no

    Trying to establish, because I don’t know, if I can simply replace the speaker with a Jensen or Weber I have on hand, or if doing so may cause some damage.

    thanks

    Larry
     
  7. NTC

    NTC Tele-Holic

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    You can use a different speaker, but you will want an estimate or measurement of the inductor value so that can be replaced as well. You might be able to get away with using a standard Fender Amp power inductor (or choke - I think I have been using the wrong term for the audience).
     
  8. printer2

    printer2 Poster Extraordinaire

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    [​IMG]



    In the Uncle Doug vid they replaced the field coil speaker and used a choke. In his test he had 277V at 38 mA so the choke would need to be rated for 40-50mA. I am thinking the 1000 on the schematic is the resistance of the choke. When Doug starts up the amp he gets around 485V on the supply which then drops to 277V when the tubes warm up. About 40V would drop across the 1k ohm field coil. You might not find a choke with that high a resistance and may have to put a resistor in series with it to make up the difference (5 H would be a good inductance). Do you know if there is anything wrong with the speaker/amp? If the speaker needs to be replaced you also have to get the right impedance speaker.

    Looking around if the feildcoil speaker is not being used replacing the coil with a 1k resistor and upping the capacitors (probably need replacing) would be the most practical thing. But you got to see what you got when it arrives.
     
    Last edited: Nov 27, 2020
  9. Wally

    Wally Telefied Ad Free Member

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    Is the field coil speaker not functional? I have a really nice Jensen F10 with the OT. The entire rig is still sitting on the baffleboard that I pulled out of an organ...all connecting wires complete. I restored a 1952 5B5 Pro that had a field coil speaker. I had to have WEber recone the speaker. Magnificent amp when all was said and done.
     
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  10. schmee

    schmee Doctor of Teleocity

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    Interestingly, I had an old Dano amp that had an inductor tranny on the speaker, but it was not a field coil speaker. I never was sure why they had it on there, I thought maybe to keep from blowing the cheap speaker? I took it off and there seemed to be no effect not having it.
     
  11. David Barnett

    David Barnett Doctor of Teleocity

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    Mounting the output transformer right on the frame of the loudspeaker was common in the 1940s and early 1950s.
     
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  12. schmee

    schmee Doctor of Teleocity

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    It wasn't the OT, more like a choke. The amp had an ot on the amp chassis.
     
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