4X12 8ohms and 4X12 16ohms question ?

Discussion in 'Cabinets & Speakers' started by Kelia, Sep 15, 2019.

  1. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    The 2555SL has an option of 16, 8 and 4 ohm secondary via an impedance selector.
    You really should not mismatch. There is no reason to do that.

    Just get the correct speaker/cabinet arrangment.
     
  2. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Once again, MARSHALL HAS NEVER INCORPORATED A VOLTAGE DOUBLER.
     
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  3. john hammond

    john hammond Well-Known Member

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    ironballs, im amazed at your knowledge.
     
  4. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I think that would depend on what pill you are on.
     
  5. South Park

    South Park Active Member

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    A parallel circuit the resistance is divided by the number of resisters . Series it adds. You can use a ohm meter just to be sure on the speaker jack . Multiple speakers make it fun
     
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  6. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    This is just something I am interested in, a hobby of sorts.
     
  7. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    That is one way to look at it. :)
     
  8. john hammond

    john hammond Well-Known Member

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    ironballs, I admire the bravery, but your boat has a hole in it, a big one.

    The presence of a centre tap seems to confuse certain people in relation to voltage doubling.
    by adding a centre tap to the standard voltage doubling design, voltage can be balanced between the two filter caps that are in series.

    example standard full wave rectifier transformer h.t taps( jcm800 50 watt marshall)

    360v-0-360v

    example marshall full wave voltage doubler h.t taps ( these are the actual values used in 100 watt marshalls jcm800 etc)

    175v-0-175v

    not a bad little iq test for the brave.

    Anyway moving on, the danger of hopping onto some kind of crazy mission to convince people that marshalls don't use voltage doubling is that you may forget the context in which you do so.

    ie : flyback voltage spikes don't care if there is a centre tap or not, the voltage that goes through that diode/cap network is doubled.

    -Challenge that if you must, good luck.

    Again, mismatch on a 100 watt jcm 800/jmp marshall made after 1968 4 ohms amp---.8ohms speaker and you will get 2000v spikes, 4ohm amp ----. 16ohm speaker will see your windings exposed to 4000v.

    - and theres plenty of 100 watt marshalls with replacement o/t's to prove it.
     
    Last edited: Sep 18, 2019
  9. South Park

    South Park Active Member

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    I do not know why Marshall built it that way. The voltage doubler is hooked to a floating ground . It is the only amp to use it .it is something to do with the pt
     
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  10. john hammond

    john hammond Well-Known Member

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    i bet it is something to do with $$$
     
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  11. Nik Henville

    Nik Henville Well-Known Member

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    Based on Jim Marshalls "design" history...

    ...this is almost a certainty :cool:

    :hippie::pirate::uk:
     
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  12. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I am only saying this once more. It is not a voltage doubler.
     
  13. SmokeyDopey

    SmokeyDopey Well-Known Member VIP Member

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    Would any of you care to expand a bit on how it is or isn't a voltage doubler?
     
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  14. john hammond

    john hammond Well-Known Member

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    smokeydopey, most people simply see that marshalls use voltage doubling in these amps, people like ken fischer himself, people like me, people who actually make amps from scratch and wish to utilize components and different types of things like rectification systems for advantage.
    There are people who , apparently, simply for the sake of it, point out that there is a centre tap and therefore cannot be a voltage doubler, because other voltage doublers dont use this centre tap.
    if you visit forums where they debate this topic, the nay-sayers will often start with " yes, they do double the voltage but if you take out the centre tap and add bleeder resistors and..and but..and"

    i read the first six words of those responses and lose interest utterly thereafter.
    Voltage doubling is good because it creates bass ( volume on ' 0 '..heard that before?) and it means iron can be smaller, cheaper ( ever wondered why 100 watt marshall power transformer is the same size as 50 watt?)
    In hi-fi its very good because one problem tube amps have is bass response, and voltage doubling gives you more of that ( hi-fi has less damaging transients than guitar amps, and they would never dream of mismatching speaker load, also, they use much higher quality iron in hifi)
     
  15. SmokeyDopey

    SmokeyDopey Well-Known Member VIP Member

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    So part of the work is done by the PT, and the other part of it is done by this doubling circuit? I'm still very new to electronics and I haven't bumped into this subject yet. Thanks for bringing this up.

    But Im curious why Mickey is saying it isn't. Because of the center tap? Still not sure how to put that together. Again, all very new to me.
     
  16. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    What I will say is go get educated in electronics so that you can figure out what is what without taking the word of someone on the internet.

    If you would rather take someone's word then so be it.

    Here is what Marshall actually did. Marshall used the two sides of the PT HT secondary as a balancing circuit just like you see stacked power filter capacitors in other amplifiers which have stacked resistors in parallel with them. It is that freaking simple and I have explained it before.
     
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  17. john hammond

    john hammond Well-Known Member

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    Sergey V Lavrov

    - “If it looks like a terrorist, if it acts like a terrorist, if it walks like a terrorist, if it fights like a terrorist, it’s a terrorist, right?”

    Maybe it would be helpful for you ironballs to view the matter in another way, for clarity..

    Seeing as you ARE educated, do you agree

    1) voltage doubling enables power transformers to be much smaller
    2) voltage doubling causes reverse flyback spikes
    3) voltage doubling adds bass response over other forms of rectification.

    It is relevant to note, there aint many fender twins that have had blown output transformers, but many 100w marshalls have had new output transformers.
    It is also relevant to note that the marshall 100 watt power transformer is the same size as the 50 watt marshall power transformer.
    And, is it just co-incidence that these marshall 100 watters sound better with the bass rolled almost off, or off entirely?
     
  18. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    There is no other way to view it unless you have a beautiful mind.
     
  19. SmokeyDopey

    SmokeyDopey Well-Known Member VIP Member

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    Thank you
     
  20. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    You get it. You see it in other power supplies. It is the same thing just using the component on hand since it has a center tap while the HT supply circuit uses the entire HT secondary of the PT for the bridge rectifier circuit.
    Again it is freaking simple yet the beatiful mind does not acknowledge what really is there.
     

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