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Is your unoptainium power switch worth $5 and an hour or so of your time?

Discussion in 'Solid State' started by K7sparky, Feb 26, 2013.

  1. K7sparky

    K7sparky AK Subscriber Subscriber

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    Location:
    Great State of West TN
    A quick look at the Littlefuse and ST data sheets show both have a linear temperature dissipation of about 1 watt per 1 A continuous RMS current within the amp rating of the device.

    If your amp gobbles up 3 amps, then the TRIAC has to dissipate 3 watts and is independent of the current rating of the TRIAC.
     
    Last edited: Jan 7, 2017
  2. c.coyle

    c.coyle Fighting the Dunning-Kruger Effect Subscriber

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    Do you feel comfortable getting them off Ebay?
     
  3. K7sparky

    K7sparky AK Subscriber Subscriber

    Messages:
    236
    Location:
    Great State of West TN
    So far have had no problems with new parts. Then again 20A 600V is so overkill what could go wrong - go wrong - go wrong - go wrong

    Got a few transistors listed on the bay as NOS and am guessing were rejects that didn't work in the switching PS from a Motorola service monitor. One of the fussiest applications I have done battle with.

    Luckily a friend mentioned the identical with higher voltage I had overlooked - again on eBay that were new run direct from BOCA Semi out of Florida which worked fine. Before BOCA they had been obsolete for years.

    I have a pile of both regular and Darlington some with Ft well into the mHz for switcher application that wouldn't work in the 20 kHz switcher that I had thought any old audio transistor would work in.

    If parts come from the other side of a pond patience is a necessary virtue.

    In general I get most parts from Mouser or DigiKey as I don't want to wait and only need a few of this and that.

    I use enough TRIACs it was worth the wait to get 50 to try and still have some of the Littlefuse ones on hand. Always feel better with more than one source.

    A few things like coated fiber glass tubing of sizes I don't have rolls of come from China / HK. Thinner than the stuff I have rolls of but fine for low voltage.

    BTW love Alfred E Newman with a soldering gun
     
  4. TenYearsGone

    TenYearsGone New Member

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    Here, There, and Everywhere
    I finally got around to trying this mod on an Akai AA-1125 with an arcing power switch, but it seems to have had no effect on the switch's intermittent buzzing. I even disassembled the switch and cleaned up the contacts with Deoxit beforehand for good measure.

    Think the switch is just too far gone at this point? I haven't had any real power issues with the unit yet, just the arcing noise.
     
  5. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    New Jersey
    Shame,
    It works well.
    Any chance the noise isn't actually the switch?
     
  6. K7sparky

    K7sparky AK Subscriber Subscriber

    Messages:
    236
    Location:
    Great State of West TN
    [QUOTE="Think the switch is just too far gone at this point? I haven't had any real power issues with the unit yet, just the arcing noise.[/QUOTE]

    I doubt you have a switch problem.

    The switch is carrying about 100mA gate current. Hopefully you have removed the old snubber(s) that reduced the switch contact arcing in the original design.

    The TRIAC turns on about 1V past zero crossing and is conducting the current your amp is actually using so no arcing noise.

    I have had similar noise now and then and generally track it to a transistor breaking down and that might look like a power supply problem especially since the noise is intermittent. Monitor line voltage and see it if shows up at higher voltage. Sometimes in completely unexpected place like the mic amp. Leaky caps are another source.

    The source can be a bear to find.

    Any chance you have a scope? Use AC coupled on the vertical and start snooping for noise. Start with the DC supplies or on the preamp output. A minimum bandwidth is all you need the noise is low frequency.

    Some other member(s) can probably suggest what they use to snoop for noise. I'm always looking for some new way.
     
    Last edited: May 17, 2017
  7. TenYearsGone

    TenYearsGone New Member

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    Thanks for the suggestions! I finally had a chance to do some more troubleshooting, and it turns out the residual "buzz" was coming from the nearby power transformer. It seems that both the switch and transformer were previously buzzing together, so I was still left with a bit of transformer noise after I fixed the switch issue with the triac. I removed the transformer from the chassis, installed rubber washers on the bolts, and tightened it back down. Now the receiver is noise-free and back to work in my second system. As countless others have mentioned in this thread, this triac mod works like a charm!
     
    nj pheonix likes this.
  8. K7sparky

    K7sparky AK Subscriber Subscriber

    Messages:
    236
    Location:
    Great State of West TN
    Strange. Has someone had the transformer out before you got the amp?
    Most amps and a fair amount of test gear have Nylon T washers at minimum under the bottom and a lot have them top & bottom. The bolt holes in the iron are usually larger than the screw allowing the bottom of the T to slip in & center the screws. Flat washer on top to protect the Nylon on the bottom maybe yes maybe no the chassis has plenty of surface area.
     

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