2555X Gain difference between power modes

Discussion in 'Marshall Amps' started by JacksonCharvelAddict, Sep 6, 2019.

  1. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025
    I know that pentode mode and triode mode sound very different in the Jubilee. The triode mode is darker and smoother and feels like it is a little looser than the full power mode. The other day I noticed after switching to the full power mode that the gain seemed to be substantially higher than it was in triode. Is there actually more gain to the full power mode or is it just the extra mid range that makes it appear there is more gain?
     
  2. Kelia

    Kelia Well-Known Member

    Joined:
    Feb 26, 2018
    Messages:
    1,199
    Likes Received:
    1,293
    I don't know what the answer will be but I'm 90% of the time playing on low power mode ,
    I love the sweet woody tone I get out of it , sounds like Page Madison Square Garden !

    My amp is a 2555SL and need to pinch myself to stop playing !
     
  3. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025

    Hell yeah bro. I love the low power mode too. I use it to get a Metallica black album kind of tone. With hit pickups its super saturated and dark but smooth and clean at the same time.
     
    Mitchell Pearrow and Kelia like this.
  4. Kinkless Tetrode

    Kinkless Tetrode Well-Known Member

    Joined:
    Aug 17, 2017
    Messages:
    1,350
    Likes Received:
    1,839
    I'm wondering if the tighter, punchier, low end and the extra zing in the top end when in pentode is giving the impression of more gain?

    Maybe it is hitting the speakers harder?

    I used to use the low power quite a bit. I liked the woodier mids and softer top end. Now I rarely use it. I started hearing what it did to the low end almost all the time-and not liking it.
     
  5. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025
    That is another possibility. I know the speakers can add break up when driven harder.
     
  6. headcrash

    headcrash Active Member

    Joined:
    Jun 19, 2015
    Messages:
    160
    Likes Received:
    232
    Technically speaking, the low power switch does nothing to the preamp, but simply switches the power stage pentodes to triodes.
    Assuming you compared similar volume levels, the slightly darker tone you (and we) are experiencing, might result as a kind of low-pass-y behaviour of the triode mode. That might blend out some of the overtones of the distortion and thus might give the impression of less gain.
     
    JacksonCharvelAddict and Kelia like this.
  7. Kelia

    Kelia Well-Known Member

    Joined:
    Feb 26, 2018
    Messages:
    1,199
    Likes Received:
    1,293
    Played my 2555SL yesterday considering the OP's question and
    the gain is the same , just more beef coming through and blending with the gain imo !
     
    JacksonCharvelAddict likes this.
  8. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025
    I think you guys are right. I think the pentode mode is just fuller and it filters some of rhe high mids out. I still enjoy the triode mode quite a bit. I EQ both modes totally differently. Its almost like a new amp in each mode. Thanks for all the comments guys!
     
    Kelia likes this.
  9. Lance Chambers

    Lance Chambers Well-Known Member

    Joined:
    Jun 23, 2019
    Messages:
    1,719
    Likes Received:
    2,741
    Location:
    The Land That Time Forgot
    I'll say this: there sure are a lot adjectives used in this thread.

    :agreed:
     
    JacksonCharvelAddict likes this.
  10. Geeze

    Geeze Well-Known Member

    Joined:
    Jul 25, 2015
    Messages:
    1,567
    Likes Received:
    2,861
    Location:
    Floating around TN in Marshall Heaven
    I've never jelled with the triode mode - I stuck in KT66's for a darker, smoother sound with better note separation. They're on the warm side of bias though - I'd like to find a circuit diagram to change out the bias resistor. The 2555 is different.

    Russ
     
  11. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025
    Yes this is totally true. I was hoping someone with knowledge of the circuit could tell us if the drive is affected by the power mode. I know that when I got the amp the bias was way off and it made the amp sound terrible.
     
    Lance Chambers likes this.
  12. Kinkless Tetrode

    Kinkless Tetrode Well-Known Member

    Joined:
    Aug 17, 2017
    Messages:
    1,350
    Likes Received:
    1,839
    Most of the gain and distortion in a Jubilee is created in the preamp, with V1 being cascaded plus the LED network. However, just like most Marshalls the hotter the signal from the preamp that hits the power amp, and the higher the output master is turned up, the more the power amp starts to overdrive and compress. That is a factor in the total Jubilee tone equation, proven by the fact that they usually sound better up loud. Changing power tube types, and the bias setting on the big ones, makes a difference to the distortion character of a Jubilee as well.

    The 100 watt Jubilee power amp is the same basic design as a JCM 800 2203. Triode mode is simply the screens being connected via the high/low switch to the plates, making them functionally an extension of the plate. So you have three elements; the cathode, the control grid, and the anode or the plate. In pentode, the screens are independent of the plates, causing the tube to function more efficiently producing about twice as much power. This might be producing more gain, but not necessarily more distortion. There are more harmonics, too, as an empirical observation.
     
    Last edited: Sep 8, 2019
  13. The Greek

    The Greek Member

    Joined:
    Apr 10, 2011
    Messages:
    42
    Likes Received:
    22
    Location:
    Thessaloniki/GREECE
    Absolutely normal and it's my experience as well. I think it's the relatively higher frequencies that are in play when in 100Watt mode which can be perceived as a little more gain. Remember that back in the days when distortion and overdrive units were not invented yet, they used treble boosters (Dallas Arbiter Rangemaster) for more gain. Both modes are super useful. And it's the exact same case with the original Jubilees also. I have a 2555 and a 2554 Silver Jubilee combo and they behave exactly the same in that regard.

    Couldn't have said it better.
     
    JacksonCharvelAddict likes this.
  14. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,077
    Likes Received:
    12,032
    Location:
    US of A
    The idea behind half power Triode and full power Pentode is that say you want to achieve 50W, in Pentode at 50W output you have a cleaner fuller more detailed sound while of maxing out in Triode at 50W the preamp and PI are tilted pushing the power tubes with more overdrive/distortion.

    Also to note is that Pentode operation is more efficient with more headroom while the Triode mode is less effecient which lends to the bit darker sound.

    Always: additional reserve power equates to more power concentration to everything especially towards higher frequency output and low frequency control.
     
  15. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025
    I really think the triode mode sounds good at low volumes. It also makes a lot of sense that a low power mode would have less high end. I definitely just think its a difference of EQ rather than actual gain.
     
    marshalltsl likes this.
  16. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,077
    Likes Received:
    12,032
    Location:
    US of A
    I agree Triode mode does sound good at lower volumes but at lower volumes you are not pushing much therefore it is a cleaner signal.

    When it comes to less or more high end its kind of like this, you notice the more you turn up a car radio, a stereo or even sometimes a musical guitar amplifier that most people reach for the BASS and TREBLE knobs. At high volumes people tend to turn the TREBLE down some while increasing the BASS a bit.
    That is because higher frequencies are more efficient and more easily magnified/amplified. It takes way more power to increase the volume of low frequency. So for example in simple terms if you turn the volume up a bit it may be noticed that the bass is maybe twice as loud while the treble frequencies are 4 times louder.

    On my vehicle's strereo system is the programmable EQ which I have dedicated 5 memories. Each memory has the same bass and midbass levels but as I go from memory 1 to memory 5 the mid through high frequencies are increased respectively.
    So EQ memory 1 is for blasting out the neighborhood (has lower dB level settings for mid-high) at maxed volumes while memory 5 is for low level listening with the windows rolled up.
     
  17. JacksonCharvelAddict

    JacksonCharvelAddict Well-Known Member

    Joined:
    Mar 4, 2016
    Messages:
    1,890
    Likes Received:
    2,025
    That's awesome that you have a neighborhood blasting setting..lol
     
  18. nix_gibby

    nix_gibby Active Member

    Joined:
    Jan 13, 2019
    Messages:
    119
    Likes Received:
    242
    Hey Greek, can you compare 2555x with 2555 and 2554? I mean in every aspect, not only the power modes.
     
  19. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,077
    Likes Received:
    12,032
    Location:
    US of A
    Well I save that for the highway but you get the idea.
    I can be heard for blocks.
     
  20. El Gringo

    El Gringo Well-Known Member

    Joined:
    Jul 24, 2015
    Messages:
    2,203
    Likes Received:
    2,236
    Location:
    Shakedown Street
    I like how you explained that . Thank You .
     

Share This Page