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SWR red face 350 vs. Ampeg B5R

Discussion in 'Amps and Cabs [BG]' started by Ampegged Paul, Sep 9, 2008.

  1. Ampegged Paul

    Ampegged Paul

    Jun 17, 2008
    in 2 parts...
    I have an opprotunity to buy a SWR(tube pre-amp) then I would sell My Ampeg. So heres my questions:
    #1)How is it that my Ampeg is 500W@2 ohms and 300@4 and the SWR is 450@2 and 350@4? Im a scientist as my day job and I swear the "amp math" gets me all the time.
    #2)Is it an upgrade to go from the Ampeg B5R to the SWR?

    Thanks guys!:bassist:
  2. pbass2go


    Dec 19, 2004
    Apple Valley, MN
    1. Amp math has always been a mystery with some companies giving inflated numbers and so forth.

    2. I am not familiar with with the ampeg amp but I have heard the red faced 350 and it sounds great. It should have enough power to push a 4X10 and have a direct out for a PA.

    Good luck
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    I wouldn't think of the swap as an upgrade, so much as a change, (for better or worse). Only you will know if the SWR is "better".
  4. Ampegged Paul

    Ampegged Paul

    Jun 17, 2008
    I was more lookin for opinions or any practical advice about the SWR(It'll be my first...maybe).
    I play through an Ampeg 410HLF and a GK 410 backline. So it seems like Im down to 350 preamp tube watts from the SWR or 300 from the solid state Ampeg.
  5. lundborg


    Apr 8, 2008
    I've used the SWR red face for almost 10 years now... A great little amp! I use it with an Ampeg 1510 cab (15" + 4x10"). This is an 8 ohm cabinet so the output power should be about 240 w.
    For the small places I play it's just about enough.

    I think there is some risk that you might find it slightly underpowered compared to the 500 W Ampeg. Also, I think the SWR is a bit sensitive to overheating. Definitely I wouldn't run it @ 2 ohms, and I've drilled large holes in the rack case for cooling. (The fan noise is a bit disturbing sometimes BTW).

    As for the amp math, you have two main factors I think:
    - The PA supply voltage, which limits the wattage at high impedance load.
    - The power rating of the mains transformer (in VA), which limits the wattage at low impedance load.

    So when you have a high impedance speaker, the PA starts to
    clip before the transformer core becomes saturated, and vice versa. Hence the different output power rating/impedance relation for different amp brands (assuming the figures in the spec are true).
  6. Ampegged Paul

    Ampegged Paul

    Jun 17, 2008
    God bless ya Lund. I took calculus 1,2 and 3 in college and I couldnt figure that out.:rollno:
    I believe both my 410's are 8 ohm so...doesnt that make it a 4 ohm load on the amp because I have two?
    Wheres my slide rule?
  7. Gearhead43


    Nov 25, 2007
    With your two 8 ohmers you'd be running the head at 4ohms.

    I use an SWR Bass 350 and it rocks. I have no problems with it at all.

    Do some research on SWR amps here, I found some good info. There are some tips here that will help you get the most out of it. I've also never heard they were prone to overheating, the amp chasis is aluminum and acts as a heatsink so they are designed to get hot, and they have a 2-speed fan. From other info I've read they can run at 2ohms quite happily.
  8. lundborg


    Apr 8, 2008
    It's good to hear that you can run it on 2 ohms safely... I never
    dared doing that...

    When I got my 350 (almost new but used), it sounded a little
    bit distorted... Instead of bringing it back to the dealer, I took the lid off and found a power resistor rattling around.

    The PA had overheated to the extent that the solder melted. So either they had been running it with too low impedance speakers, or mounted it in a closed box. I soldered the resistor
    back, and the amp has been working perfectly ever since
    (on 8 ohms mostly).

    The SWR:s have one major design flaw IMO, that the air is
    drawn from side to side (instead of front to back). Which means
    that if you mount it in a stock rack casing, the fan will be
    feeding the heated air back into the amp. So you need some
    holes on the side of the case to let the hot air out.
  9. tcrouzzz


    Jul 12, 2009
    I have a red face SWR that runs 450 watts RMS @ 2 ohms. I'm using a swr junior goliath 4 ohms and a ampeg 8 ohms w/ 2 12'. Can anyone tell me what the ohms in this case are in total? I use to be good at math but that was a while ago... The issue is that my amp get's very hot and I'm wondering if I need to change the speaker combo? Thanks

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