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Author Topic: blower noise  (Read 2373 times)

Posts: 1

« on: July 10, 2004, 10:34:29 AM »

I recently acquired a Henry 3k Premier 8877 Console. The mechanecal noise from the blower is louder than I
am on SSB. Has anyone changed the blower yo something
else, or have another solution.Thanks

Posts: 9749


« Reply #1 on: July 10, 2004, 11:22:02 PM »

As a long time designer of amplifiers, the number one complaint for adequately cooled amplifiers is noise.

People seem to forget the amplifier is generating just as much heat as RF output power, if not more! Most of the heat is in a very compact area, it is in the tubes.

If you are running 1500 watts, the tubes are almost certainly making 1500 watts of heat. The only way that heat gets out of the amplifier is via air movement.

You normally have to move at least 50CFM of air to have modest temperature increases of 100-200 degrees in air temperature, and if you move it through a tube anode the air system HAS to make noise. There is no way to efficiently move air through a blower and tube cooler without turbulence, and that causes noise.

So you have a decision to make, and it can only be your decision. You can move less air, you can add low restriction noise baffles, you can buy an expensive blower (like the ones Ameritron uses in the AL1200 and 1500), or you can do a combination.

Whatever you do, I surely hope you or whoever helps you knows enough about airflow to not run the seals in your tubes over temperature by making a mistake in airflow!

What I'd suggest is getting a cardboard tube like out of a roll of paper towels, and listening through it while hunting for the major source of air noise. Then at least you know if it is turbulence in the tube coolers or the impeller of the blower making the noise, and you have some idea where you will have to work.

You could also buy a cheap sound meter from Radio Shack, and use it.

73 Tom

Posts: 21764

« Reply #2 on: July 12, 2004, 11:20:50 AM »

The Henry design also makes it reasonably easy to "remote" the blower elsewhere.  You still have noise of the air rushing through the tube, socket, chimney and enclosure and exhausting out the top, but the noise is much less than when the blower sits under the tube in the same room with you.

With several Henry console amplifiers, I've "remoted" the blower using a 240V line cord (the blowers in their big amps are all 240V-only), a suitable socket and plug, and 3" or 4" flexible dryer hose, like what is used to exhaust the hot air from a clothes dryer, and hose clamps.  In one case, I had my shack in the garage, and the blower was even too noisy for me there, so I put the blower in the laundry room adjacent to the garage, in a closet, with the blower mounted in an enclosure about 10" square having a dryer vent on one side (blower exhaust) and a grilled opening covering one whole side of the enclosure (blower inlet).  I eventually changed the grill to a window screen material, which acted as an air filter to help prevent blowing all the dust in the house back into the amplifier.  That meant cleaning that screen periodically, maybe once a month.

When I would flip the power to the amp "ON" for shack visitors, they were always impressed how quiet my Henry amp was.  Then, I'd open the door to the laundry room and listen to how loud it used to be!


Posts: 85


« Reply #3 on: July 12, 2004, 01:44:47 PM »

Another sourse for tubing to "remote" the blower can be found at a well stocked pilot shop. Look for the orange scat tubing used in many aircraft.

Posts: 9749


« Reply #4 on: July 16, 2004, 08:27:39 AM »

You have to be careful remoting a blower, or doing any airflow mods.

It would be a good idea to measure the pressure drop across the tube socket and cooler (anode) to be sure you haven't reduced airflow significantly. You'd be amazed at how much airflow resistance ductwork can have.

A pressure interlock isn't a bad idea, in case the blower power is cut off or the ductwork has a problem. At the very least, keep a watchful eye/ear on the system.

8877's aren't cheap.

73 Tom
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