[Amps] Acoustic Noise Comparison

[Jim Barber]

I'd hate to warp the cover MIG welding, but then I'm no welder at all - 
just guessing.
Also - just read your last... Angle stock would be stronger, but we're 
trying to dampen resonance. my seat-of-the-pant-ometer says flat bar 
would be perhaps just as effective and would have a flatter profile.

I hate to admit this in public, but the last one I fiddled with I used 
1/2" MDF in strips, first sealed with a 50% solution of yellow glue and 
water, then glued (press-clamp HARD) to the underside of the cover with 
Gorilla glue. I spent too much time "cutting and trying", but in the end 
it worked well and although I haven't heard that it's ever come off, it 
would be non-conductive if it did. I'm planning the same treatment for 
*my* QRO HF2500DX, which suffers from a cheap-but-easy-to-replace, 
solid-mounted Dayton blower and a huge sheet metal cover. That one's 
also getting an EBM-Papst ball-bearing unit with a cast housing, 
assuming I can make it fit.

Just some ideas - there are some bright people that read this list, 
perhaps one or more of them will share a relevant experience.

73,
Jim N7CXI

On 6/21/2012 3:12 PM, Jerry Kaidor 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.
> *** I do have some "Dynamat" left over from a car project.  I might try
> a few pieces of that stuck to the top & sides - in places where there's
> nothing for it to short out if it comes loose - which doesn't seem very
> likely; the stickum on Dynamat is extremely agressive.   The casing is
> pretty thick metal - but it sure does ring like a bell when you tap it.
>
>> Better blower mounting and fuzz would help a lot, a scattering of braces
> *** By "braces" I assume you mean narrow strips of metal welded to the
> case so they stand up at right angles to it?  My cover has a couple real
> good
> scratches in the top, so it needs to be bodyworked anyway.  Unfortunately,
> according to Mr. Magnet, it's aluminum.  I do have a spool gun for my MIG
> welder that's supposed to be able to weld aluminum, but I've never tried
> it yet.  And that's assuming it's a weldable *alloy*.
>
>     The amp came to me without rear feet, so the back of the cabinet is
> resting on the desk.  I have ordered new feet from RF Concepts, along
> with the new blower.
>
>                              - Jerry Kaidor
>
>
>