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Distance between transformers

Discussion in 'Amp Tech Center' started by ponce, Dec 1, 2018.

  1. ponce

    ponce Tele-Holic

    Age:
    39
    567
    Dec 21, 2011
    Croatia
    How far apart should the power and output transformers be placed to avoid interference. Does orienting them in 90 degree fashion really help with hum/noise?
     
  2. Old Tele man

    Old Tele man Friend of Leo's

    May 10, 2017
    Tucson, AZ
    Yes for 90-degree orientation.

    Distance is function of how BIG magnetic fields each generate...so, BIG output transformers are spaced further apart than smaller output transformers...basically an I-squared times L function.
     
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  3. ponce

    ponce Tele-Holic

    Age:
    39
    567
    Dec 21, 2011
    Croatia
    What about their influence on tubes?
     
  4. Old Tele man

    Old Tele man Friend of Leo's

    May 10, 2017
    Tucson, AZ
    "Inverse-Square Law" applies to both electric & magnetic fields.
     
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  5. ponce

    ponce Tele-Holic

    Age:
    39
    567
    Dec 21, 2011
    Croatia
    Is it safe (soundwise and safetywise) to move the power transformer off chassis and mount it somewhere else in the cabinet with longer wires?
     
    Last edited: Dec 1, 2018
  6. ponce

    ponce Tele-Holic

    Age:
    39
    567
    Dec 21, 2011
    Croatia
    I ask this because I want to install 2x10" speakers in a 1x12" combo and the power transformer is kind of in the way.:)
     
  7. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    You mean like this?

    upload_2018-12-1_18-29-1.jpeg
     
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  8. ponce

    ponce Tele-Holic

    Age:
    39
    567
    Dec 21, 2011
    Croatia
  9. dogmeat

    dogmeat Tele-Holic

    Age:
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    Oct 12, 2017
    Alaska
    put headphones on the output trans and listen for a quiet orientation with the power tranny on
     
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  10. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Yeah I was going to suggest putting an ac voltmeter on millivolt range on the OT primary while rotating it around to find the lowest reading.
     
  11. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    I have mounted them in the same orientation in custom builds with no apparent problem. They were probably 3" or more apart though.
     
  12. Old Tele man

    Old Tele man Friend of Leo's

    May 10, 2017
    Tucson, AZ
    Quick-n-Dirty "eye-ball" experiment...put a cheap Boy Scout Compass nearer and nearer to any transformer to get a idea of "how close" is too close...you'll know when the compass doesn't point North any more.
     
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  13. wanderin kind

    wanderin kind Tele-Meister

    Age:
    63
    281
    Apr 24, 2018
    Olympia WA
    xfmr.JPG how many turns? induced voltage is proportional to turns, got a Marshall with 800 turns or a Fender with 4000 turns?

    how big is the power transformer? the bigger the better for keeping stray flux inside the core. Permeabillity drops as the E-I lams get smaller. Dinky pwr xfmr gonna radiate a lot, look at a Marantz 2270, pwr xfmr is right next to RF input, so they use a huge core and low turns to keep radiation down.

    having iron at opposite ends does help balance the weight,

    other types of noise will dominate transformer coupling, listen to Pete Townsend and tell me what the worst noise is,
     
    Last edited: Dec 3, 2018
  14. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    As much distance between transformers as possible is a good thing, but not always ideal if it means running the HT B+ lines and high current output secondaries in the vicinity of the preamp.

    On the other hand, the conventional 5E3 has its OT and PT almost adjacent to one another, oriented 90 degrees apart. With proper grounding, they are dead quiet.
     
  15. Wyatt

    Wyatt Tele-Afflicted

    Nov 3, 2004
    No, generally not safe or desirable. A lot of precautions would have to be met. Are you building from scratch or modding an existing amp?Mush easier to design an amp to be built this way from the start.

    Better solution would be to buy/build a custom 2x10 cab. Otherwise, many 2x10, 4x10, or 2x12 have offset baffles, with one speaker lower than the others to clear the iron.

    [​IMG]

    Even Fender did this...
    [​IMG]
     
    Last edited: Dec 6, 2018
  16. telemnemonics

    telemnemonics Doctor of Teleocity

    Age:
    59
    Mar 2, 2010
    Maine
    I've moved an OT over a little on the chassis to clear a bigger speaker magnet, did it with the amp on so I could hear the hum change, but then of course shut it off before drilling new holes!

    Moving the PT to fit more speakers in a cramped cab?
    There are more wires to the PT and some are carrying killer voltage, I'd buy another cab before relocating the PT.
    Or choose one of the tens with a smaller magnet?
    Many alnico speakers have removable covers over the magnet and I've removed them for this issue, as did Fender in the Tweed Bassman and other amps.
     
  17. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec

    Some vintage amps, such as Magnatones and just about every vintage organ I've seen do this, but the PT is always in a chassis of some kind. Just taking it off the chassis and bolting or screwing it somewhere and lengthening the leads is very dangerous.
     
  18. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    If it's done safely and correctly, sure. If done haphazardly, then no. As you can see from the pic of the Excelsior I posted, they mounted it very securely and used conduit to route the HV wires to the preamp chassis.
     
  19. ponce

    ponce Tele-Holic

    Age:
    39
    567
    Dec 21, 2011
    Croatia
    I've moved the PT successfully, made a new baffle, installed the 2 tens only to find out that they sound like crap. Back to 1x12", and hopefully a new amp one day. This one gave me too much to do last 10 years.
     
    Last edited: Dec 6, 2018
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