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Guess which ALS-600 transistor was bad

Discussion in 'Amateur Radio Amplifiers' started by KQ0J, Feb 25, 2021.

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  1. KQ0J

    KQ0J XML Subscriber QRZ Page

  2. KQ0J

    KQ0J XML Subscriber QRZ Page

    Hint: all 4 were but the last one exploded to let me know it was time to replace them....
    K0UO likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What was the cause of failure?
  4. AI3V

    AI3V Ham Member QRZ Page

    Why were there transistors from different manufacturers in there?

    Thats not right.

    You want 4 "matched" transistors (usually they are matched for dc beta) and they should be from the same manufacturer and lot.

    Has this amp been repaired before?

    K0UO likes this.
  5. K4MP

    K4MP Ham Member QRZ Page

    You need to lap the heatsink as in this W8JI video

    Heatsinks were improperly machined causing poor heat conduction and transistor failure.


    KT4RAM, K0UO and K4YNZ like this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The only reason I don't favor SS power amps is they're generally air-cooled and the fans make noise.

    Now, if they were liquid cooled, that would be quieter (and also run the transistors cooler).:)

    I've had a project brewing (in CAD only, not built) for a couple years for a liquid-cooled SS HF amp. Not as difficult as a water-cooled tube amp because the voltages are much lower and if the coolant becomes slightly contaminated...kinda "so what?":p But I never actually did it (yet). Might make a great retirement project, if I can still have access to the CNC VMCs I have access to now, to machine the ductwork in the heatsinks; I'd use copper, not aluminum, and not only "machine" the mounting surfaces, but probably EDM and polish them.
    KD2ACO likes this.
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Regale us with pictures if you do this. Sounds like fun!
  8. AI3V

    AI3V Ham Member QRZ Page

    The heat sink is fine.

    Somebody botched the previous repair job.

    Unless Tommy is putting floor sweepings in new amps...

  9. AG5CK

    AG5CK Premium Subscriber QRZ Page

    My tube amp is in the garage and I can hear it in the living room. That way I don't forget to turn it off.
  10. WB4ZLU

    WB4ZLU Ham Member QRZ Page

    Yes Steve. Life is tough without a VMC and CNC lathe w/ live toolong.
    W1TRY likes this.

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