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FatBoy 4 Pill 2879 small cabinet specs

Discussion in 'Amplifiers' started by Prof. Base, Nov 24, 2021.

  1. Prof. Base

    Prof. Base New Member

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    Does anyone know what the minimum & maximum input dead key for this amp? I emailed the FatBoy manufacturer too and was unable to get a response.

    Thanks in advance.
    FATBOY AMP.png 20211120_055137[1].jpg


     
    #1 Prof. Base, Nov 24, 2021
    Last edited: Nov 24, 2021

  2. groundwire

    groundwire Sr. Member

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    25w per transistor OUTPUT max. So 100w output carrier from the amp is as high as i would push it. The amp experts will show up soon with the transistors specs to give you exact drive levels. Or just look up the transistors specs yourself.
     
  3. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    Your going to get different answers because there are different 4 x 2879 configurations.
    A biased 4 transistor amp will react differently than a class c amp.
    That's a class c comp amp built for AM using HG transistors.
    In general you can start here.......
    No more than what ever it takes to get a 100 watt dead key max as groundwire posted.
    I suggest no more than 40 watts peak drive max, that's 10 watts peak drive for each 2879 to start.
    How you go up from there is up to you, but this should be a "safe" starting point.
    I have run Toshiba's harder than this in class c , but I have not run any HG's to to the failure point so I would limit them to that.
    Bare in mind that you would not run a Texas Star or similar amp like this.
    Maybe Crusher will see this and jump in, he has more experience with the HG transistors but this should give you a starting point.

    73
    Jeff
     
    Prof. Base likes this.
  4. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    How much you drive it with depends on how long you want it to last. When you notice the output is a little lower than it used to be, and you turn up the drive to compensate, it is the beginning of the end for those transistors.
     
    NZ8N and Prof. Base like this.
  5. groundwire

    groundwire Sr. Member

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    i keep all my B biased hg 2879 boxes at 125w pep per device and i have had zero problems for many many years now. no heat issues, gain loss etc. when in doubt just mentally copy texas star output specs, ie: 2x2290 = 250w pep, 2x2879 = 350w pep, 4x2879 = 500w pep, 8x2879 = 1200w pep and so on. it has worked for me just fine when in doubt for hg's
     
  6. Prof. Base

    Prof. Base New Member

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    I should have my Stryker 655 back soon. It's getting a lil' more PEP in it's step.
    I'm taking the advice from everyone and just combining it. Gonna play it safe and use a 2-4 watt dead key from radio and just let it swing from there.
     
  7. 144inBama

    144inBama Sr. Member

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    Don't go any lower than 1 watt out of the radio, it will affect you audio. Use the variable on the box to set the dead key to 100 watts
     
    Prof. Base likes this.
  8. kc8mob

    kc8mob Active Member

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    The weak link in a short glance in that box is the relay.

    If you drive the piss out of the amp. Which you will. That's the whole point. It will draw every bit of 70 amps or more from your power source.

    So at 50% efficient overall, half of that "visualized" picture of power is going to go through that litty Itty bitty relay. Granted it's a voltage not current scenario. But that just makes chewing up the Itty bitty relay contacts happen faster.

    4 2879s need to be run through a relay that goes "thunk"

    That relay would be good for switching bias on when you key up.
     
  9. kc8mob

    kc8mob Active Member

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    Well crap. I'm not here to make you feel bad about your linear. As you mentioned you got no response from the "builder" or dealer/seller.

    If you have a radio tech you know, trust. Have him put a 10$ relay in the amp. Even use the small one to trigger the big one.

    They used metal clad caps on the output tx's so they know what can't be skimped on. And yeah. You have time before the little guy welds itself.

    It's just i hand build amplifiers in the music industry and I absolutely hate my own business, but damnit! Why can't OEM's do it right?

    Well I'll tell you. In the CB/free bander market they offer no real warranty.

    I do. And I never ever have to do warranty repair because I know that you don't make any money going back to the same job twice. So. Build it right. And charge the schmucks buying it accordingly for you having built it right.
     
    NZ8N likes this.
  10. Prof. Base

    Prof. Base New Member

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    My tech buddy took a look at the box and just said, and I quote,

    "No more than 100 Watt carrier, SWR of 1:3 or less, and you should be fine, Don't be afraid to baby it. I'd do 60 watts carrier on the amp and leave your variable on the radio alone once it's set. Don't worry about your 100 watt PEP swing. Modulation never killed any of my amps, but too high of a carrier and you're gonna smoke it. This one could pull close to 50-60 cups of juice depending on your swing. Don't do anything stupid and play music with it." End quote. Play music...Nope! rofl.

    He's primarily a vacuum tube type guy, but I find merit in his advice because it coincides with some of the info I got from you guys. Much appreciated.
     
  11. Highway Man

    Highway Man Well-Known Member

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    I won't buy a Fat Boy middle man box because it's a box of secrets. He won't show the inside of it. And like said above the dime store relays are lacking. From my end the only inside glimpse of a Fat Boy I get is on 3 Made's repair bench and lack of QC that goes out the door
     
  12. Highway Man

    Highway Man Well-Known Member

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    That box with the variable is most likely a driver box. It was never intended to be driven like a comp box.thus the baby relay. 500-700w is what the target is
     
  13. Prof. Base

    Prof. Base New Member

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    Well for whatever reason, it's running just fine with my Stryker 655. 6 watt DK input, 40 watt amp DK, 14.3 v input, swings to 350. I'm babying it.
     

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