[Boatanchors] [Hallicrafters] got the HT-20

[Robert Kerr]

Perhaps the warping is from thermal stress in the casting, possibly from 
cooling it too fast when the part was made, or not annealing (heat 
treating) it to relieve the stress after fabricating.  It's like the S 
meter cases in every SX-28 receiver I've ever seen.  The meter cases and 
face enclosures were made from a single part by putting brass tubing in 
a punch press.  For the wartime effort to manufacture as many SX-28 
receivers and possible and get them into service, they probably didn't 
take the time to anneal the meter cases to relieve the stress imposed by 
the press.  Now, almost 70 years later, every one of those brass meter 
cases I've seen is cracked open in 15+ places, because of the stress 
concentration lines in the metal crystal structure imposed by the press.

Bob K4ERR

On 06/19/2010 09:35 PM, Robert Nickels wrote:
> On 6/19/2010 12:53 PM, Brian Harris wrote:
>    
>>    I wonder if the much touted SX-88 has the same cheesy bezel.
>>      
> Some did, but not all.  I don't think any of us ever conclusively traced
> the problem to a specific group of serial numbers, although if anyone
> would know, it would be Hank Arney who (while the rest of us were
> whining!) took the initiative to work with a CNC machine shop to have
> new ones manufactured, and they turned out great.   The bezel warpage
> was a result of insufficient stress relief in the original castings -
> over time those stresses simply twisted the bezel up like a pretzel.
> You can't get much "earlier" than my SX-88 as it was one of several
> hand-built prototypes and it had the warped bezel problem, but I've know
> other early s/n owners say theirs are fine.    Evidently the supplier
> fixed the process or Hallicrafters found a new one, as the majority of
> these bezels (including the one on my HT-20) seem to be OK.
>
> A ham buddy from southern Illinois told me how one guy he knew made a
> wooden pattern and sand-cast his own SX-88 replacement bezel out of
> melted-down aluminum scraps.   I recommend the CNC approach ;-)
>
> 73, Bob W9RAN
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