[Amps] Acoustic Noise Comparison

[Carl]

My 76PA 3 holer is almost silent, same sheet metal

Carl


----- Original Message ----- 
From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
To: <amps at contesting.com>
Sent: Thursday, June 21, 2012 9:05 PM
Subject: Re: [Amps] Acoustic Noise Comparison


> On 6/21/2012 2:43 PM, Jim Barber wrote:
>> Spot on, Jim.
>> The 76A and the 78 suffer from both vibration and turbulence, with the
>> effects compounded by resonances in the sheet metal cover.
>
> My "old" 76A is almost silent with no vibration in the cover.
> For those that do vibrate, a simple piece of tape on the top of the
> center partition should quiet it as it has to vibrate against something.
>
> If the fan vibrates bad enough to make the case vibrate enough to make
> noise I'd check the squirrel cage to make sure there is nothing going
> for a ride. Those fans are very sensitive to any foreign material...
> like bugs.  I can lay my hand on the case while the fan is running and
> feel no vibration and that thing is so old that any rubber is long gone.
>
> And for Jim? Mig welding from a spool is often an exercise in futility
> and frustration.  Heat and speed are critical and I'd not weld anything
> to the cover anyway.
>
> 73
>
> Roger(K8RI)
>
>>
>> Better blower mounting and fuzz would help a lot, a scattering of braces
>> in different lengths (where they'd fit) under at least the cover top
>> would help them help.
>>
>> Some may not believe this, but after bracing, bead-blasting and
>> powder-coating the top cover with heavy wrinkle-black helps at least a
>> little with the cover resonance(s).
>>
>> My .02,
>> Jim N7CXI
>>
>> On 6/21/2012 9:28 AM, Jim Brown wrote:
>>> On 6/21/2012 10:12 AM, Jerry Kaidor wrote:
>>>>      Still playing with my "new" Alpha 78.
>>> No experience with that amp, but some components of motor noise are
>>> vibrationally coupled to the desk or shelf that the amp sits on. I've
>>> reduce that component of the fan noise in my Titan 425 amps by setting
>>> the RF deck on soft foam padding. There are no vents on the underside of
>>> that amp, so I'm not interfering with cooling.
>>>
>>> I bought all of my 425s used, and one of them came with a power
>>> transformer that made a lot of noise. The problem was loose windings, so
>>> I jammed some shims between the windings and the frame to kill the
>>> vibration.
>>>
>>> Another component of fan noise is air turbulence, and the components are
>>> higher in frequency.  Higher frequency components bounce off of hard
>>> surfaces (like walls and shelves) and into the room. We can kill those
>>> reflections (and thus some of that noise)  by placing soft materials
>>> (what we acoustic consultants generically call "fuzz") on those
>>> surfaces.  Obviously this should be done in a manner that doesn't
>>> interfere with cooling.
>>>
>>> 73, Jim K9YC
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>>
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