Ameritron 811h fan mod

Discussion in 'Amateur Radio Amplifiers' started by W5DWR, Oct 10, 2010.

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  1. W5DWR

    W5DWR Ham Member QRZ Page

    I read on a review about the 811h that there is a drop-in replacement fan sold by Radio Shack. Does anyone happen to know what the part number of the fan is?

    Thanks and 73,

    Don - w5dwr
     
  2. W8JI

    W8JI Ham Member QRZ Page

    The much better question is, "Why would someone want to replace the fan with one from Radio Shack and what is that fan's ratings?" :)

    I found the review but I would not change the fan uless you change to 572B tubes, and unless you are sure the fan really does have more airflow. More air flow will NOT improve ratings or life of the 811A tubes.
     
    Last edited: Oct 11, 2010
  3. W5DWR

    W5DWR Ham Member QRZ Page

    The amp does have 572b tubes, and if I can find the part number I can check the specs for it and make sure it moves more air before I do any changing. It sounded like a good idea at the time :rolleyes:

    Don - w5dwr
     
  4. W8JI

    W8JI Ham Member QRZ Page

    It could use more air if you are going to hammer the 572's.

    I would make sure, against about .025 inches of backpressure, it has more airflow.
     
  5. W5DWR

    W5DWR Ham Member QRZ Page

    Thanks, and I don't hammer the 572b's. Like I said, it sounded like a good idea at the time. Maybe not :cool:
     
  6. W4AFB

    W4AFB Guest

    The amp has more then adequate ventilation as long as you dont block the intake on the side of the amp. And unless you arent tuning the amp correctly your only going to run the 572b's so hard with 1800 plate volts. No need to re-invent the wheel.
     
  7. W8JI

    W8JI Ham Member QRZ Page

    More cooling is always better for components, although the difference is probably not ever noticable in normal use.

    When I design things like that (I designed that amp and many others) for amateur, noise is always a major concern. Noise is always a major complaint no matter how quiet an amp is.

    Because of that, I always set airflow the minimum required at 5000 ft altitude. Unless you run the 811H hard with bigger 572B tubes, the extra cooling won't do much. If you change the tubes and hammer it the weakest link is tank coil cooling and transformer temperature, so more airflow helps that.

    73 Tom
     
  8. W5DWR

    W5DWR Ham Member QRZ Page

    When I tune the amp, I tune to 600 mA of plate current and 150 mA of grid current, so pushing too hard is not a problem. I think I'll leave everything as is. Thanks to everyone for your input.

    73,
    Don - w5dwr
     
    Last edited: Oct 11, 2010
  9. W0UZR

    W0UZR Ham Member QRZ Page

    As long as we're talking about the 811H cooling system, I have a question. My fan in the back is not blowing the air out. It's blowing the air in. And the hot air comes out the vent holes on the side. Is my fan in backwards?
     
  10. W0UZR

    W0UZR Ham Member QRZ Page

    When I tune my amp, I turn up the drive to where both of the meters are almost pegged, then when I adjust the plate and load then they come down, then turn drive up again to where they are almost pegged again and adjust plate and load again. But DO NOT spend anymore than 2 or 3 seconds on each adjustment and unkey right away! Then when it's all tuned up, I turn my drive down to where the meters say where the book says to have it during operation, about 475ma current and 100 grid, then I turn the load up a little more (Not Much) to get the grid to drop, then adjust the plate again for peak and also look at the grid when retuning the plate to adjust for lowest on the grid while keeping the peak power output up. The lower the grid, the better your tubes will last.
     
    Last edited: Oct 12, 2010
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