Half Power Switch on Marshall 2555 Jubilee

Discussion in 'Amps and Cabs' started by Ronstrat63, Feb 18, 2008.

  1. Ronstrat63

    Ronstrat63 Member

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    I love my tone from this amp but find the half power switch on my 100W head pretty useless. At the low power setting the amp sounds thin and lacks punch. It sounds much better with switch on full and the master rolled back.

    I have an Airbrake which at two clicks down has the same volume as the switch at half power but sounds so much better (actually pretty close to unattenuated).

    Is this my amp or is a problem with the switch circuit design?
     
  2. blackba

    blackba Supporting Member

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    I have a marshall 2553 (50Watt) and I also find the half power switch robs tone like you are describing, I think it is just the amp design. I haven't seen a schematic to know what the half power switch is doing....
     
  3. Ronstrat63

    Ronstrat63 Member

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    I thought it turned off 2 tubes out the 4.
     
  4. JerryP

    JerryP Member

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    The half power switch is a triode/pentode switch. At half power all 4 power tubes are running as triodes.
    Jerry
     
  5. Troser

    Troser Member

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    Pull the inner or outer tube pair, and cut the impedence in half... for instance, pull the inner pair, and switch to 8 ohms while plugged into your 16-ohm cab. That'll give you a lot more growl and sing at slightly-attenuated volumes.

    I've got the same head too. ~Tim
     
  6. Ironman

    Ironman Member

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    High power (pentode) sounds best...that is if you want the most balls out of her. Triode mode is too soft and just overall lacking for me.
     
  7. mmorse

    mmorse Member

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    I have a 2550 and experience the same thing. I also had a little Winfield head that had a half power switch. It too suffered when in half power. I think it's just the way the whole pentode/triode thing works. At half power it's not that much lower in volume but it thin outs way too much. It loses the grunt and lower mids. I'll bet it's even worse with the 100 watt.

    As a rule it's the same difference I hear between 50 watt and 100 watt Marshalls. The 50s are almost as loud as 100s but they lack the nice, full grunt and authority of a 100 watter. Of course I'm talking when both amps are turned up.
     
  8. Ronstrat63

    Ronstrat63 Member

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    I think that a 50 Watt head would sound much fuller than a 100W head in Triode Mode.
     
  9. s2khawk

    s2khawk Member

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    its one of the only bad designs in that circuit besides the diodes all over the crunch channel. I've never heard any guitar amp sound decent in triode mode and thats what 'half power' does here, I mod that switch on the 100watters to just go down to two tubes. If you go to two tubes, you should also switch the speaker out to half of where it was at full power, fyi.
     
  10. soldano16

    soldano16 Member

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    I once asked my amp tech about a 1/2 power switch. He refused. Said they never sound good.
     
  11. yZe

    yZe Senior Member

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    varaible voltage regulation (VVR) & power scaling (PS) is it

    I'm done w/ attenuators and pen/tri reduction (which was on a demeter I owned)
     

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