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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    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

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

    K7sparky AK Subscriber Subscriber

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    [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!
     
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  8. K7sparky

    K7sparky AK Subscriber Subscriber

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    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.
     
  9. c.coyle

    c.coyle Fighting the Dunning-Kruger Effect Subscriber

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    Just a note that Tayda Electronics currently (2017-07) has ST Microelectronics BTA24-600CWRG Triacs (600V 25A) for $1.54 U.S. That's 50 cents cheaper than Mouser or DigiKey. These are the snubberless models for inductive loads, with the insulated case.

    I have ordered small parts from Tayda maybe half a dozen times, and had no problems. Shipping isn't the fastest, but that's about my only gripe. I have no connection to these folks.
     
    Last edited: Jul 12, 2017
  10. K7sparky

    K7sparky AK Subscriber Subscriber

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    Tayda out of Thailand has given me excellent service also. Anything off shore is slow. But old IC especially CD4xxx off shore are not only cheap, they may be the only source and usually top manufactures. Had great luck.

    Tayda has a USA presence in Colorado I think. They are a bit more $ but a lot faster on what they have as they are stateside. thaishine on fleabay. Another stateside vintage parts seller that has been a continued reasonable source and fast shipper is huskerfan42011.

    I have had need for a lot of vintage chips lately on several projects and been blessed with good prices and supplies

    The BTA TRIACS you mentioned have soldiered on just fine for me. Just as good as the littlefuse I started with and ALWAYS more comfortable with a second source. Anyone had any problems with them?
     
  11. c.coyle

    c.coyle Fighting the Dunning-Kruger Effect Subscriber

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    They came the other day, and they are a lot smaller than the comparable Littlefuse triacs. This will allow me a couple good locations on a Pioneer SX-636, where a Littlefuse wouldn't have worked.
     
  12. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    I opened up a dead Dremel rotary tool recently and found it uses a TRIAC to provide motor speed control. The interesting thing is it had an odd diode-like device in series with the gate of the TRIAC. Looking that up on the web led me to discover it was a DIAC and it helped smooth out the AC pulses coming into the gate.

    http://www.radio-electronics.com/info/data/semicond/diac/diac.php

    @Hipocrates has convinced me to give the TRIAC switch thing a try and since I've got some DIACs here now I'll include those and see if anything changes.

    Here, hold my beer....
     
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  13. Hipocrates

    Hipocrates AK Subscriber Subscriber

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    :beerchug:
     
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  14. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    @EchoWars please help me sift through the many posts here in this thread. You said you had installed two of these TRIAC mods like in post #34 but without the snubber and it has been working fine. What did you mean by "without the snubber?"

    1. Did you mean you eliminated the resistor and the cap between MT1 and MT2?
    2. Or did you mean you just eliminated the cap between MT1 and MT2 and the resistor between MT1 and MT2 is still used?

    Thanks!
     
  15. merlynski

    merlynski Curmudgeon Electronicist Subscriber

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    [​IMG]

    The snubber is the resistor and cap across the switch contact (left side of drawing), it reduces the arc pulse created when the switch opens, protecting the switch contacts.
    The resistor on the gate of the triac (right side of drawing) is required to trigger the triac. Since the triac is rated for inductive loads without a snubber the snubber can be eliminated.

    Drawing credit to K7sparky, post #1
     
    Last edited: Aug 10, 2017
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  16. K7sparky

    K7sparky AK Subscriber Subscriber

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    merlynski got it correct:beerchug:

    What ever your amp had across the power switch for arc suppression remove it when doing this mod. Most designs used one piece RC snubbers. A few just used a .01mFd cap. It will do no good and may do harm.

    Pay attention to the type of TRIAC. Most are not designed for inductive loads. The original TRIACS needed snubbers to survive an inductive environment and the snubber design could be problematic. Note a few of the early posts form members that had problems before the inductive rated TRIACS were around.

    Your not doing voltage level control. Just switching on or off.
     
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  17. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Got it. Thanks.


    Ah, so just buying a TRIAC with sufficient voltage and current handling is not enough. I'll dig deeper into the prior posts and try to determine what to look for that tells me "this particular TRIAC is good with inductive loads." The one I've purchased clearly states that in the datasheet, but I'd like to understand enough to look for it in listings. From my datasheet:

    "Teccor offers bidirectional alternistors with current ratings from 6 A to 40 A and voltages from 200 V to 1000 V as part of Teccor's broad line of thyristors. Teccor's alternistor is specifically designed for applications that switch highly inductive loads."​

    The circuit in the HK330B that I'm working on looks like this:

    Slide1.PNG

    And my plan is to change it to this:

    Slide7.PNG

    Am I on the right track?
     
  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Take a look at your 'after' diagram, ;) it isn't the same as the one in the first post (the same diagram is posted in post #175). :)
     
  19. dlucy

    dlucy dlucy67 (Doug) Subscriber

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    Thank you!
     
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  20. c.coyle

    c.coyle Fighting the Dunning-Kruger Effect Subscriber

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    I'd do it like this. It helps me to think of the triac in series with the hot side of the primary. I also like the fuse before the switch.

    EDIT: Corrected drawing below, to properly show switching between Gate and MT2.

    Triac corrected.jpg
     
    Last edited: Aug 11, 2017
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