[Amps] Acoustic Noise Comparison

[Roger (K8RI)]

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
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>