Need Fan upgrade for Al-811 due to heavy FT8 Duty Cycle

Discussion in 'Amateur Radio Amplifiers' started by K4ZOT, Sep 9, 2018.

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  1. KI4AX

    KI4AX Ham Member QRZ Page

    And don't worry about all the great contacts you are NOT getting, and cannot hear, because you decided to spend the money on an amp instead of a better antenna...

    Dan KI4AX
  2. K6BRN

    K6BRN XML Subscriber QRZ Page


    I don't know WHAT you're using, but QRZ seems to show you aren't making many contacts. So maybe you should get one? Or operate more. Either works.

    I'm using an amp, sometimes with a pretty good antenna and sometimes with a compromise antenna at a 2nd QTH with HOA restrictions. The amp lets me work what I hear. So, the right tool in the right situation. Is using a better antenna wise? Sure, if it's practical.

    And it's really not about money. Lot's of us on these forums have BAGS of money (in stocks, bonds, bank vaults, etc.). We don't get out much - nothing to spend it on. Glued to the computer and can't get up, anyway. So why not have a good antenna AND and amplifier.

    OK... done pulling your leg. :) (in the last paragraph)

    Brian - K6BRN
  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    Wow! Running a continuous carrier digital mode like RTTY or FT8 QRO with an 811 amp. I'm impressed. It's kind of like driving a Yugo downhill toward a tree at 90 MPH. If it can even get there, there's a pretty good chance the ending won't very happy, because the brakes just aren't up to the task.

    Hmmm. The 811 tube (this is where I get into deep trouble with the venerable tube amp crowd) is rated (by RCA) at 45 watts PLATE dissipation, CCS (which is what you'd BETTER go by for RTTY/FT8 QRO). The amp uses three 811s and is about 50% efficient (give or take), so what you put out is about what the tube plate dissipates (just a rough estimate, guys and gals). 3x45=135 watts continuous would (usually) be a reasonable safe high duty cycle TX limit estimate. For the 811H amp, 4x45=180 watts.

    Higher and tube life is shorter. But at some point, given the 800 is not a graphite based tube capable of standing overstress for very long... POP! at some unknown point a bit over that.

    But then, there's the sheer thrill of not knowing. I get it!
    KJ4VTH likes this.
  4. KJ4VTH

    KJ4VTH Ham Member QRZ Page

    I still don’t get it. QRP level signal works for me. Sorry to hear more are not similarly encumbered. :)
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    All depends on antennas.

    When I first got on PSK31 many years ago (the long-ago forerunner to FT8:p) I found if I used more than about 10W TX power everybody complained, and at the time the complainers were in Europe and Asia. But I was using beams on towers, not dipoles in attics and such.

    It's all really "e.r.p." related. 10W to a 20m beam at 60' may well be equivalent to 200W to a compromised dipole or vertical surrounded by junk.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    ERP was great using a 8 element Wilson Shooting Star on 11 meters legally.
  7. K4ZOT

    K4ZOT XML Subscriber QRZ Page

    Just worked Albania on 40M - with my modest station and 300 watts. I'll stay at 300 watts with my dipole. Just need to work zone #23 for my WAZ.

    My Amp heat issue was getting the heat OUT of the Amp because it is located next to a shelf upright. I have cut a hole in the upright and installed a nice muffin 50 cfm fan. It has made a word of difference - temperatures are way down.

    Tnx for the advise.

    WAS, WAS-6M, VUCC (272 grids confirmed), WAC, DXCC (208 entities confirmed), WPX
    Last edited: Sep 17, 2018
    KA9JLM likes this.

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