>

Marshall Haze 15 - Everything you wanted to know...

Discussion in 'Marshall Amps' started by Micky, Oct 28, 2014.

  1. Pete Farrington

    Pete Farrington Well-Known Member

    Joined:
    Jan 18, 2021
    Messages:
    529
    Likes Received:
    522
    This thread was cited by a recent thread, so as it's turning up in searches, I thought it would be a good idea to clarify some points.

    The stock 6V6 didn't look like JJ to me, Chinese manufacture seems more likely.
    As they had seen a couple of years service, it's not valid to then state that they were set at the factory to the low idle cathode currents mentioned. Valves wear out, they change with use and eventually fail, hence them being socket mounted.
    To know how the bias is set by the manufacturer, it's best to ask them, rather than attempting to work it out by analysing a product that's been in use for some time.

    It depends what anode dissipation limit has been chosen, and what % idle dissipation has been selected.
    It seems that almost all online bias calculators are grievously flawed, as their default settings for valve type selection make no distinction between design centre and design max anode limit ratings. Whereas in reality, there's nearly a 20% difference.
    All 6V6 have the same anode absolute limit, it's just that under the design centre system it comes out at 12W, whereas under the design max system the exact same anode comes out at 14W.
    The design max system was introduced in 1958 and was used by some manufacturers for some of their valve types.

    It's not obvious to me. Please review your rationale.

    What definition of 'headroom' are you using?
    All else being equal, valve gm (and hence stage gain) increases with anode current.

    No, anode dissipation at idle is unrelated to audio power output. I think that is at the root of a fundamental misconception.

    Vintage type OTs use less efficient magnetic materials for their laminations, eg M6 silicon steel. More recent material grades are more efficient, eg M29. So modern OTs can be smaller than equivalently rated vintage types. But they might give different tonal results at higher power outputs when fitted to amps, due to the different shapes of their BH characteristic curve.

    From the schematic kindly provided in post #39, R18 and R21, the 1ohm cathode current sensing resistors for the output valves, look to be rated at 0.25W. As P = i x i x R, 0.25 1ohm resistors are ok up to 0.5A! So even if a 6V6 shorts badly, those resistors should cope, especially as the voltage across them can't exceed the voltage drop of their protection diodes D9 and D10.
    Note that they're in series with the current flow, not shunt (parallel).

    May be thinking of adjusting bias by the elimination of 'crossover distortion' (as seen by displaying the output signal waveform on an oscilloscope)?
    A signal generator, oscilloscope and a dummy load are needed for that method, so it's a bit too involved for regular amp users. Plus it's easy to set the bias too hot, so it should really be checked afterwards, using the idle anode dissipation method.

    I think that is to be expected with a 15W amp.

    For the anode / HT voltages mentioned, that 7.5W is heat dissipated at idle by the valve. It's unrelated to audio power output. When an amp is generating an audio power output signal, by definition, it's not idling.

    I hope tha above is helpful, sorry to go on, and apologies to @Micky I'm not picking on you. If you're happy with the sound then it's fine to use a cooler bias, and enjoy the benefit of a longer valve life :)
     
    Last edited: Jul 5, 2021
    fitz288 likes this.
  2. Micky

    Micky Well-Known Member VIP Member

    Joined:
    Apr 29, 2010
    Messages:
    21,153
    Likes Received:
    17,891
    Location:
    Vermont
    So what EXACTLY are you saying about my calculations and observations?

    Do you have a Haze 15?
     
    fitz288 likes this.
  3. fitz288

    fitz288 Well-Known Yinzer Silver Supporting Member

    Joined:
    Apr 7, 2020
    Messages:
    3,039
    Likes Received:
    7,177
    Location:
    rahndahbaht dah 'Burgh
    Last edited: Jul 6, 2021
    Mitchell Pearrow likes this.
  4. Micky

    Micky Well-Known Member VIP Member

    Joined:
    Apr 29, 2010
    Messages:
    21,153
    Likes Received:
    17,891
    Location:
    Vermont
    I think we all have a soft spot for this amp. It is a hidden gem in the history of Marshall amps, and I will never part with mine. It is too great an amp in a small format, it can go anywhere and stack on top of almost anything.

    Thanks for your comment. It means a lot to me.
     
    Mitchell Pearrow and fitz288 like this.
  5. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409
    prolly the least talked about marshall amp and i dont know why?
     
    fitz288 and Mitchell Pearrow like this.
  6. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409
    looked up the 15 on youtube just now.
    this guy made anything sound good. whatever happened to him?
     
    fitz288 and Mitchell Pearrow like this.
  7. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member VIP Member

    Joined:
    Jul 2, 2018
    Messages:
    14,959
    Likes Received:
    29,382
    Location:
    Moreno Valley CA
    That guy made the Dsl40c sound phenomenal, and that led me to this forum 5 years ago, I know I have only been a member for 3 years, but I did a couple of years lurking ..
    I have never had the opportunity to play through a Haze though..
    Cheers
     
    scozz and ricksdisconnected like this.
  8. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    25,768
    Likes Received:
    33,120
    Location:
    Los Angeles
    at the time Chris was there, there was a revolving door & he used it...

    He was a touring musician, & they got Steve. I think that Nick Bowcott filled in for a little while, but, he used the revolving door too...
     
  9. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409

    yeah i like chris's playing. always something good from him. is he doing videos with anybody else now do you know?
     
    Mitchell Pearrow likes this.
  10. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409

    and we are glad your here bro....even if you are a couple yrs late. :cool:
     
    Mitchell Pearrow likes this.
  11. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member VIP Member

    Joined:
    Jul 2, 2018
    Messages:
    14,959
    Likes Received:
    29,382
    Location:
    Moreno Valley CA
    Thanks Rick
     
    ricksdisconnected and scozz like this.
  12. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    25,768
    Likes Received:
    33,120
    Location:
    Los Angeles
  13. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409
  14. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409

    dude was/is to amp demos what Pete Thorn is to pedal demos. simply the best.
     
    Mitchell Pearrow likes this.
  15. Pete Farrington

    Pete Farrington Well-Known Member

    Joined:
    Jan 18, 2021
    Messages:
    529
    Likes Received:
    522
    That the technical rationale displayed there within seems, for the points noted, unsound.
    No, I do not.
     
  16. scozz

    scozz Well-Known Member Gold Supporting Member

    Joined:
    Jul 20, 2008
    Messages:
    5,161
    Likes Received:
    12,007
    Wow! :rolleyes:
     
    ricksdisconnected and fitz288 like this.
  17. Micky

    Micky Well-Known Member VIP Member

    Joined:
    Apr 29, 2010
    Messages:
    21,153
    Likes Received:
    17,891
    Location:
    Vermont
    Why does no one speak of this amp?

    Because it didn't have a standby switch.
    Everyone dissed this little amp because it wasn't a 2204 and was only 15 watts. It had built-in effects and that is a no-no for a Marshall.
    Any number of reasons it didn't catch on.

    Marshall has a bunch of these 'hidden gems' in their lineup.

    Chris was the one that got me hooked with his videos of the Haze 15 and the DSL40c. He is a great player and a fantastic guy that could make any amp sound great. He has a knack for emphasizing what sounds great on an amp and can show you with a specific song or style. The guy is legendary in my opinion.
     
  18. fitz288

    fitz288 Well-Known Yinzer Silver Supporting Member

    Joined:
    Apr 7, 2020
    Messages:
    3,039
    Likes Received:
    7,177
    Location:
    rahndahbaht dah 'Burgh
    I love my Haze15.
    Chorus and reverb are my go to flavors - straight in, this amp has everything I want for tone.
    The OD channel and effects are my benchmark when I'm dialing in pedals on my other amps.

    20210702_235216_HDR (002)-s.jpg
     
  19. ricksdisconnected

    ricksdisconnected Well-Known Member

    Joined:
    Aug 11, 2019
    Messages:
    9,981
    Likes Received:
    16,409
    one bad ass amp
     
    Mitchell Pearrow and fitz288 like this.
  20. Evgen

    Evgen New Member

    Joined:
    Jun 25, 2021
    Messages:
    4
    Likes Received:
    5
    Hello everyone! I recently bought a Marshall Haze 15 amp. I really loved its clean channel and how it started to clump as the volume increased. But the overdrive channel was a disappointment for me, since there was not enough high frequencies at any position of the treble control. And then I decided to make a simple mod described here on the forum, namely, I changed the capacitors C58 and C59.
    I can't imagine that these small changes can affect his sound so much! After this mod I got a great overdrive channel! Now it sounds like JCM 800! It is very cool!
    P.S. I can't understand why Marshall engineers spoiled the overdrive channel so much.
     
    Mitchell Pearrow likes this.

Share This Page