Running 16 Ohm Speaker Into 8 Ohm Amp

Discussion in 'Marshall Amps' started by Peter Karakondis, Aug 12, 2019.

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  1. john hammond

    john hammond Active Member

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    Ok I'm gonna go off topic here because we need to talk explosions I think.

    They sort of make an exploding sound when cap cans pop...but uh...before the chinese whispers get too crazy and our amps get outlawed..the amp doesn't explode...just the cap can...just the cap can..
     
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  2. john hammond

    john hammond Active Member

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    The DEVIL will appear if you mismatch speaker loads..things will explode..there will be fire on your ass and in the sky...donkeys will walk upright..everything will blow up!
     
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  3. Dmann

    Dmann Well-Known Member

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  4. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    That is a voltage doubler.

    But this is not.


    upload_2019-8-13_21-35-20.png
     
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  5. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Not one is learning from you especially me.

    Flyback from either of the transformers is only part of the issue which causes spikes. The upward secondary mismatch also forces higher voltage on the OT primary.
     
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  6. john hammond

    john hammond Active Member

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    dude, youre showing me a picture of a schematic titled ' unicorn incorporated 1959 marshall' and now you're trying to tell me that schematic is the one that represents for example a year 1969 plexi...everybody know..everybody..that the 1968-1969 plexi has voltage doubling, it has two cap cans for the h.t two cap cans for the screens...both sub circuits utilising voltage doubling..where you get your info from is none of my business...the 66-67 plexi has a power supply like the one you've pictured, however as you'll note, I've stated these amps arent included in voltage doubling with marshalls.

    Subsequently, I simply can't read anything you type out and respond to it, it's just crap, sorry.


     
  7. john hammond

    john hammond Active Member

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    " Not one is learning from you especially me"

    - refer to my post 66.

    read, learn..then get back to me.
     
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  8. john hammond

    john hammond Active Member

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    taken from solodallas history of marshall...i told you bud, you're making a fool out of yourself.

    VERSION 5A: VERY FIRST SUPERLEADS AND SUPERBASSES, YET LAST JTM45S: THE INTRODUCTION OF DUAL RECTIFIERS (LATE SPRING 1967)
    These amps were the very first Superleads and Superbasses, yet the very last JTM45s. They have JTM45 faceplates, gold Superlead or Superbass backplates (with two fuses) and block end aluminium chasses. On the Superlead (1959) model, a 5000pf bright cap was introduced, giving a brighter and more aggressive tone. With the exception of the bright cap, the bass model (1992) used the same circuit as the lead amp – something that was also the case earlier with 100W, 50W and JTM45 amps. The Super PA and Super tremolo amps also used the same circuit, except the use of 470K mixer resistors instead of 270Ks on the PAs. PA amps also left out the 500pf cap at the mixer resistor (a cap that makes one channel brighter and the other darker).

    The Drake 1202-119 output transformer was still used on these amps, but a different power supply was introduced with the Drake 1203-80 power transformer (2.5” stack). The 1203-80 has two 95VAC secondaries that are feed to two different voltage doubler (bridge) rectifiers. After rectification each rectifier delivers around 250VDC for a total of ca. 500V. Although this voltage is high, good EL34s can usually handle it. The power board on these models have dual rectifiers and 8 32uf capacitor. Also, the single 16uf preamp filter cap is replaced by a dual 32uf cap (occasionally a dual 20uf).

    These amps are the second generation of EL34 amps with serial numbers in the low 10.000 series. Headcabs used both the narrow vent found on earlier amps and the wide vent used on later amps. It is uncertain is any of these amps had steel chassis like the later amps did. It is not perfectly clear why Marshall changed the power supply significantly on the 100W amps (but not the 50W amps). Although the new power transformer (1203-80) has a smaller stack than its predecessor (1204-43), it still delivers sufficient power while reducing the total voltages slightly (something that is good for tube life).
     
  9. john hammond

    john hammond Active Member

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    " https://marshall.com/marshall-amps/marshall-workshop/faqs/impedance

    http://blog.hughes-and-kettner.com/ohm-cooking-101-understanding-amps-speakers-and-impedance/

    https://www.mesaboogie.com/amplitud...er-impedance-matching-and-hook-up-part-1.html"

    Do you think these documents, prepared solely in order to deal with creating some weaseling room for warranty claims have a) any bearing on the subject or b) any effect on me?

    I assure you they don't.
    will they have an effect on anyone else reading?
    - probably for about ten minutes..the strongest critics of the notion that you can use speakers this way will be the first to try it.
    None of the responses trying to disprove the notion have any weight..as I'm reading these posts the bullshit-o-meter is pushed to the right hand side...especially from mdog5...he's just pulling bullshit out of the ether, making it up on the spot and trying to use mis-information to cover his ( exposed ) ass.

    What the nay-sayers really need is a post that reads something like this.. " i mismatched my speaker load and it blew up the transformer on my 1987 amplifier."

    we haven't seen these responses, remarkably considering the millions of amps that are out there...because it simply doesn't happen.

    If someone says they mismatched and then popped a tube, I'd believe that but respond with.." the tube was weak"...in effect the mismatch was doing you a favour by pointing out the dud.

    Your 500ma fuse will save you in this scenario..

    mismatch and enjoy your amps people and..your welcome.
     
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  10. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Two capacitors does not mean voltage doubling.

    It seems have total misunderstanding.

    By the way please show us this Marshall schematic that utilizes voltage doublers.
     
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  11. john hammond

    john hammond Active Member

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    here you go, i couldnt get much 100 watt diagrams, so ceriatone it is
     
  12. john hammond

    john hammond Active Member

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    diagram was too large...don't worry friends..i'll find another..do you guys...erm..work on amps?
     
  13. john hammond

    john hammond Active Member

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    The problem I'm having is that the metroamp site doesnt have its diagrams up, and the diagram i have here is saved as pdf, which i dont know how to export to here.

    But hey, don't beleive me, go and talk to another person that works on old amps..i'm surprised neikeel hasn't pitched in here...don't worry mdog5..you may just learn something today after all.
     
  14. john hammond

    john hammond Active Member

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    from ken fischer himself..enjoy.

    (B) Plexi's had less filtering in power supply, so replace 50u/50u by 20u/20u or 30u/30u and cut100uF down to 50's in series voltage doubler. By doing this we're making the power supply less stable, so if subharmonics start creeping in and you don't like 'em then increase filtering in preamp back up a bit.
     
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  15. john hammond

    john hammond Active Member

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    written by ' grosh_guitars ' on metroamp forum

    - " Late '66 to early '67 Transistion to EL34's, steel chassis and gold rear panel. Earliest JMP's.

    Still 2" Drake OT, the 1202-119 (8,16 and 100V taps) or 1202-132 (4,8,16). Both with 1.7k primary. Sometime in '66 the Drake 1203-80 voltage doubler PT came in to use. More research needed on PT's.
    Filtering now is 100,100, 32,32, 32 (mounted on chassis), 16,16 (on board).
    470k mix resistors. 56k/250pf tone stack. .1uf PI caps."
     
  16. john hammond

    john hammond Active Member

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    you want more or you done?
     
  17. john hammond

    john hammond Active Member

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    just so you know..this is the type of voltage doubler in marshalls.

    0301.gif
     
  18. WholeLottaGlove

    WholeLottaGlove Active Member

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    I was under the impression for the longest time that I could use the 8 ohm out of my amp into a 16 ohm cab... until I saw smoke. I’ll never do it again.
     
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  19. john hammond

    john hammond Active Member

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    what amp was this..how long?
     
  20. john hammond

    john hammond Active Member

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    what popped? did you fry the power trans? output?did you see the devil?
     
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