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AL-572 check out forward needle

Discussion in 'Amateur Radio Amplifiers' started by W8NIC, Nov 10, 2019 at 2:36 PM.

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  1. W8NIC

    W8NIC Ham Member QRZ Page

    Doesn’t matter how much drive and output, the needle goes nuts when transmitting on cw mode. The forward (kw) needle slams to the right. Anyone know why?
    Thanks!
     

    Attached Files:

  2. N8FVJ

    N8FVJ Ham Member QRZ Page

    Amp could be oscillating. Try tuning with more capacitance on the load capacitor. More capacitance would mean about 50 watts less output for starters.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The meter indications posted indicate a terrible SWR.

    The FWD power is an indication for FWD + REF, always, so it can read >>1kW when the output power is <<1kW, if REFlected power is high enough.

    Try it with a good kW-rated 50 Ohm dummy load and see if it reads more normally.
     
    WA7PRC likes this.
  4. W8NIC

    W8NIC Ham Member QRZ Page

    so I tried it on a g5rv jr and a hustler 6btv, both hooked up to a palstar AT4K, swr at 1.1 to 1 and still the needle slams the wall. hooked up to a palstar 50 ohms dummy load, same results. Good output at 1kw with 60w drive. With amp on stand-by, radio at any wattage, needle does the same thing, pointed straight up on dead key.
    Could it be a bad meter?
    Sorry for the stupid questions guys, I don't know much about amps.
    Please help.

    Thanks.
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    How old is the amp ?

    Did you do the normal MFJ QC checks before power up ? (Loose screws, Extra screws, Solder connection inspections...)

    Good Luck.
     
    KD2ACO likes this.
  6. W8NIC

    W8NIC Ham Member QRZ Page

    Don’t know, I just got it not to long ago .
     
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Did it ever work correctly?
    Sounds like IC301 on the meter board may be toast.

    Is the meter pinned all the time when the amp is on?

    AL-572 meter board.jpg
    click for bigger pic

     
  8. W8NIC

    W8NIC Ham Member QRZ Page

    meter is pinned only when transmitting, it's a zero when unkeyed.
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No, it wouldn't be the meter itself -- that's very unlikely.

    That meter is driven by an active circuit which makes it a "PEP" meter and there's a problem on that board.
     
  10. W1QJ

    W1QJ Ham Member QRZ Page

    There is an adjustment for that meter. It could be mal adjusted.
     

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