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Low power out

Discussion in 'Amateur Radio Amplifiers' started by N0YPD, Aug 24, 2019.

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  1. N0YPD

    N0YPD Premium Subscriber QRZ Page

    I am running an Ameritron Al-811 amp, and when I first bought the amp 3 or 4 years ago it would put out 600 watts no problem,but lately the most I can get out is around 400 watts.
    Tubes get weak or what else?
  2. W1QJ

    W1QJ Ham Member QRZ Page

    Yup tubes get weak
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    And running the 3-tube AL-811 at 600-watts output is a sure way to get the 811A tubes weak!

    The 3-tube AL-811 should be run at about 450-watts output and the 4-tube AL-811H should be run at about 600-watts output for best tube life. The station, on the "other" end, won't know the difference but the tubes sure will be able to tell that they are being pushed harder. Also, your electric company is going to be much happier with the higher power output (more income to them).

    Glen, K9STH
    W4NNF likes this.
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Yep the tubes get weak especially when abused.
  5. N7WR

    N7WR Premium Subscriber QRZ Page

    I've had several different amps over the years that have 3 811's. Never run any of them over 450 watts and the tubes have lasted a long time.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Just to chime in "one more time," yep, tubes got weak.:)

    What kills 811As isn't peak power, it's carrier power, like when "tuning up."

    If you get four new tubes, make sure you limit "tuning" time to about 5 seconds or so, and they can last a long time.

    Otherwise, you can replace the 811As with 572Bs (no other amplifier changes required) and they can handle long tuning times.
  7. N0YPD

    N0YPD Premium Subscriber QRZ Page

    Thanks for the help all of you. I think I will be going with 572Bs as a replacement.
  8. N0YPD

    N0YPD Premium Subscriber QRZ Page

    Thanks for the help all of you. I think I will be going with 572Bs as a replacement.
  9. KQ0J

    KQ0J XML Subscriber QRZ Page

    Even with new tubes, I only got 600W out on 80M , close to that on 160M , 450W on 20M and down until 200-250W on 10M ( with the smell of a component getting hot ) . The
    cure for the 10M issue was a new parasitic board or you can look up the change to the size of the coils on the board. As was said - go really easy on tuning up and run it lightly.

    I did go with 572b's for my 811H. An improvment in power out and less stress on me when tuning. I still run it easy though - 200 -400W.
  10. N8FVJ

    N8FVJ Ham Member QRZ Page

    Buy the 572B and never look back. Amp easily makes 800 watts PEP out with 65 watts drive using the 572B tubes.

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