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Bridging an old tube amp

Discussion in 'Amps and Cabs [BG]' started by samurai_24, Jul 12, 2005.


  1. Hi,

    I was wondering if it's possible to bridge a 2-channel tube amp. I have an older (70's?) Fender PA100 tube amplifier. It has two 1/4" output jacks and says 100W RMS (220 Peak) @ 4Ohms on the back. I would like to run this amp in to one 4Ohm cab, and would like to get the most power out of it. The only amps I've ever bridged were car amps, where you run a cable from the positive on one channel and the negative on the other channel to form one bridged channel.

    If I am running my cabinet out of only one side of the amp, I'm only getting half the power available, right?

    Thanks!
     
  2. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    nope.....

    the Fender tube stuff that i have ever seen was never stereo...i may be wrong
    and tube amps do not bridge like solid state unless there is a built in circuit...the amp back (or front) panel would say so if a bridge was possible.
    The amp wants 4ohms and the cabinet is 4ohms, what could be happier???
     
  3. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

  4. Thanks for the schematic! Too bad I'm no good at reading them! So what you're saying is that I'm getting full power from my amp regardless if I'm using one channel or two?

    So if I'm using one channel, I'm getting 100W, and if I'm using two, then I'm getting 50W (roughly) per side?
     
  5. timv

    timv Supporting Member

    Jun 7, 2000
    Chandler, AZ
    It is not a stereo amp. The two output jacks are parallel so they are connected to each other, positive to positive, negative to negative. There are two different jacks so you could hook up two 8 ohm cabinets which in parallel would equal four ohms. With a 4 ohm cabinet you can plug into either output and get full power.
     
  6. Awesome. Thanks for the help guys.
     
  7. The separate INPUT channels are just that, input. What you have is a mono powered mixer that uses tubes.
     
  8. Sorry if I wasn't clear, I was only referring to the output channels, not input.
     
  9. No, I get it. There are no 'other' output channels with your amp. It is a mono (ONE) channel tube amp with a mixer on the front end. There is NOTHING to bridge.
     
  10. Got it. TimV explained it best to me I think. There is only one output channel, but 2 jacks. :)