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Another New Texas Star DX 500V

Discussion in 'Amplifiers' started by Ranch55, Dec 10, 2019.

  1. Ranch55

    Ranch55 Well-Known Member

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    I have another Texas Star DX 500V amplifier in from a friend to take a look at. He purchased it new about 2 months ago.
    It is experiencing high VSWR's on any antenna, but almost flat on a dummy load. This information is according to an experienced tech who has already had it.
    He asked me to take a look at it.
    My initial suspicion is the DEI transistors that it came with, based on the information he provided.
    I won't have an opportunity to look at it for awhile yet.
    Keep you posted.


     
    Dmans and 543_Dallas like this.

  2. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Input tuning?
     
  3. Blackcat630

    Blackcat630 Sr. Member

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    Bummer
     
    Mudfoot likes this.
  4. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    I am becoming very disappointed with hearing this.
    It is starting to become all to common to hear this same topic on several forums.
    Not good news.

    73
    Jeff
     
  5. 2NC995

    2NC995 WDX995 / DAN

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    Weird. Interested to see what you find.
     
  6. Ranch55

    Ranch55 Well-Known Member

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    The experienced tech who initially looked at it did improve it some by working with the input tuning.
    But his info to me strongly suggests issues with the DEI transistors.
    An imbalance with the boards output into the combiner is heating up the combiner resistor, and one board is significantly heating up more than the other board.
    When I do get to it, I'll start from the beginning and remove the boards to thoroughly inspect the bottom traces for issues and work my way up from there.

    Hey Dmans, it is all interesting and enjoyable. Good talking to you on the radio.
     
  7. 999

    999 Well-Known Member

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    I would start with the capacitors on the transformers to ensure that they are all within spec....cold AND hot. If they aren't, or are and drift significantly when heated, I would replace them all and try again.
    If that fails, then I would dig deeper into the amp to see whats what. No need to make more work for yourself than you need to.
     
    2NC995 and AudioShockwav like this.
  8. Ranch55

    Ranch55 Well-Known Member

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    The previous technician has done exactly that. He is a good tech and does good work.
    But, I would do that anyway, so as to be thorough.
    I have seen this type of issue many times. It generally does end up being the transistors, tuning capacitors, or incorrectly wound transformers. I doubt it is the transformers, but that can cause the issue.
     
    2NC995 and AudioShockwav like this.
  9. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    What is sad is that the guys down there at Galaxy uh I mean Texas Star are not getting this right when they build them.
    I know that not every setup is the same but it seems that the ones built with DEI transistors are now all suspect.

    73
    Jeff
     
    2NC995 likes this.
  10. 2NC995

    2NC995 WDX995 / DAN

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    I bought mine a couple months back which puts it at close to the same age, and have to say I’ve been rather happy with it performance wise. Input SWR is excellent. Out of the box the preamp didn’t work (I’d be happy if it didn’t even have one) and the meter is temperamental (also would be happy if that were omitted). I fixed the preamp, and can’t see the meter where it’s mounted anyway so haven’t bothered.

    Have another waiting for me in the shopping cart at Copper.

    Two very easy mods that made it even better...a fan kit connected to an 1/8” jack which is controlled by the power switch, and the keying transistor removed for a direct key line from the radio so I don’t have to muck with the SSB switch or delay. Used the CW key hole for the latter mod...and love it. All “export” radios should come set up for this...IMO.
     
  11. Tokin

    Tokin 42Zero Tampa

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  12. 2NC995

    2NC995 WDX995 / DAN

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    I don’t have any complaints in my dealings with Copper. Not sure what you mean by the problem - “waiting in my cart” meant that I haven’t ordered it yet ;)
     
    Ranch55 likes this.
  13. OldTech03

    OldTech03 Sr. Member

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    What exactly are you referring to?
     
    2NC995 likes this.
  14. OldTech03

    OldTech03 Sr. Member

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    A couple of really clear up-close images of the board in the DX500 would be very helpful as well as the values of the caps that are being used on the transformers both primary and Main transformer as well as the values of the Caps being used across the Collectors to ground. The bias resistors should be looked at carefully to make sure they are actually 10 ohm.
     
    Crusher and Shadetree Mechanic like this.
  15. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    What I am talking about is that it seems more than a few 500's seem to be showing problems right out of the box with tuning issues.
    The guys down at TS should be concerned about that.
    You should not have to fix a new amp right out of the box before you use it.

    73
    Jeff
     
    CB590 and Shadetree Mechanic like this.

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