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Thread: Ameritron 811h fan mod

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  1. #21

    Default

    I came over a possible solution for even lower fan noise by using a 80mm to 120mm Fan adapter:

    http://www.cooltechpc.com/c/ctpc/std...n_adapter.html

    If I remove the internal fan and place this adapter on the outside I can fit a 120mm fan on the outside. I did find a 230V AC low noise fan which I can connect after the internal ON/OFF 230V switch. But I need to drill a hole in the back plate and run the fan wires thru a rubber insulator to go inside the cabinet. If I use extra shrink tubing on the wires I think it will be ok regarding insualtion for 230V AC.

    I will look into it.

    Best regards

    LA4AMA
    Roar

  2. #22

    Default AL-811H fan mod

    Hello.

    Now I have done the mod with a larger 120mm fan on my AL-811H.

    http://www.yourpicbox.com/images/omUqVhOXN17110.jpg

    http://www.yourpicbox.com/images/oWkxZmbzu17111.jpg

    The Fan now runs very quiet and blows more air than before.
    I did use a 230V AC fan (Papst 4890N and 23dB A). Connected fan on the ON/OFF switch inside, so it runs when turn the amp on.

    Also used small rubber gaskets (3 mm thick) underneath the transformer, and on the transformer bolt, so the transformer is "floating" and not in contact with the metal cabinet. This helped a lot on the transformer "hum" I had.

    The PA now runs very very quiet.

    Best regards
    LA4AMA
    Roar

  3. #23
    Join Date
    Oct 2003
    Location
    Middle Georgia USA
    Posts
    7,722

    Default

    How do you know it blows more air than before?

    Why is that important? id you change to bigger tubes?

    I'm not saying it isn't a good change, but did you measure anything? I think some of what you notice is from 50 Hz power mains. This slows down fans and makes transformer magnetizing current increase.
    Last edited by W8JI; 11-19-2010 at 11:42 AM.

  4. #24

    Default

    Regarding airflow I rely on the data from Papst:

    Original Fan (Papst 8800N) at 115V/60Hz: 27,7CFM , 2500rpm. 28dB A

    New Fan (Papst 4890N) at 230V/50Hz: 47,1CFM, 1550rpm. 23dB A

    For me the basic goal was to minimize fan noise and transformer hum, not actually to increase cooling. But a bit more airflow probably will not hurt....

    I am planning on switching to 572B tubes instead of the Taylor 811A tubes that is mounted in this unit now.

    My AL-811H had quite loud transformer "hum" and that was tiering to listen to. I tried to put some soft rubber sheets under it's feet but it seemed like the transformer hum did resonate the whole cabinet, and I could not get rid of it. After isolating the transformer from the cabinet the hum is now very faint.

    Best regards
    LA4AMA
    Roar

  5. #25

    Default

    Never mind, mis-read the specs. Now see 27 point 7 CFM vs 47 point 1 CFM. Thought it was 7 vs 1, duh.

  6. #26

    Default

    Quote Originally Posted by KC9LGW View Post
    the orignal fan moved 7 Cubic Feet of air per Minute and the new one moves 1 Cubic Feet of air per Minute. How is this better?
    The comma in Europe is a decimal point, when used with numbers:

    Original Fan (Papst 8800N) at 115V/60Hz: 27,7CFM , 2500rpm. 28dB A

    New Fan (Papst 4890N) at 230V/50Hz: 47,1CFM, 1550rpm. 23dB A
    This is 27.7 cfm vs. 47.1 cfm.

    However those sound like free air ratings without backpressure, which makes them a bit irrelevant. The only thing that counts is air movement with the backpressure provided by the system. In an AL-811H I have no idea what that is, but it's easy to compare air movers by installing each one and measuring the lfm at the air exhaust point(s). You don't get precise numbers this way, but you can tell if one is moving more air than the other one.

  7. #27
    Join Date
    Oct 2003
    Location
    Middle Georgia USA
    Posts
    7,722

    Default

    I looked at the data for those fans.
    http://www.ebmpapst.us/allpdfs/4000N.PDF
    http://www.ebmpapst.us/allpdfs/8000N.PDF

    At 60 Hz:

    The 811 and 811H have about the same back pressure, about .05 inches measured at 15 CFM when the cover is on.

    The 8800N is 28 dBa noise and about 17 CFM at .05 inches.
    The 4890N is 25 dBa noise and about 22 CFM at .05 inches.

    The new fan looks a little better as long as the outlet restriction doesn't reduce flow from the new fan.

    As Steve says, they have to be compared at actual back pressure.

  8. #28

    Default

    Thanks for that info about back pressure.

    One other thing I noticed is that the outlet from the original fan is rather close to the transformer (about 1.5 inches).

    http://www.yourpicbox.com/images/oGMtcGQsJ17125.jpg

    I dont know if this has anything to say for back pressure, but with the new fan on the outside the distance from fan adapter outlet to the transformer is about 2.5 inches. Also, the adapter will probably also give some restriction and also increase outlet airspeed because of the cone shape.

    Best regards
    LA4AMA
    Roar

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