[ARC5] Front panel widows

[Michael Bittner]

OK, thanks Mike
Mike, W6MAB
  ----- Original Message ----- 
  From: Mike Everette 
  To: Michael Bittner ; Brian ; arc5 at mailman.qth.net 
  Sent: Saturday, February 04, 2017 4:16 PM
  Subject: Re: [ARC5] Front panel widows









  Mike Bittner asked:

  I'm wondering if different materials were used for the ARC-5s than the ATA 
  and SCR-274 based on the excellent shape of the ARC-5s as compared to the 
  otthers.  Maybe they were just exposed to different conditions, or maybe 
  they are not all cellulose acetate?


  WA4DLF observes:

  I have several ARC-5 transmitters which were overhauled by the Navy during the fifties; in two cases they were painted grey.  The windows are in perfect condition.  On the other hand I've seen other ARC-5s (not ATAs or 274s) where the windows are shriveled and crystallized.  These don't have overhaul dates or tags.  So my contention is that the "good" ones are very likely replacements.


  73


  Mike


  WA4DLF




























  ----- Original Message ----- 
  From: "Brian" <brianclarke01 at optusnet.com.au>
  To: <arc5 at mailman.qth.net>
  Sent: Friday, February 03, 2017 5:45 PM
  Subject: Re: [ARC5] Front panel widows


  > The original window material in the Command transmitters and BC-221 family 
  > was nitro-cellulose acetate - the basis for early cine film. The original 
  > solvent gradually evaporates, leading to physical distortion and 
  > coloration. You could smell the solvent in the early cinema projection 
  > rooms. The degradation is not reversible. The observation that a solution 
  > was to buy up old stock transmitters to scavenge their windows will not 
  > beat the natural chemical and physical degradation.
  >
  > The better solutions emerging from this discussion are the use of Perspex, 
  > Lexan, other clear cyano-acrylates and polycarbonates, though even these 
  > will change shape over time. Plenty of this material is used for 'gels' 
  > over follow spots for stage shows - and so becomes a cheap source of our 
  > raw material. Think how sexy your transmitters would look with yellow, 
  > green, blue and red windows!
  >
  > The scales and numbering on the Command transmitters varied between 
  > manufacturers and most definitely with operational frequency range; on the 
  > lower frequency models, the markings were closer spaced. So, the 
  > possibility of making 'one size fits all' is a forlorn hope.
  >
  > My solution was to photocopy an engineering mm scale onto clear plastic 
  > and cut to fit. Cheap and cheerful. In the old days of Drawing and Design, 
  > scales with all sorts of spacings and numberings were available.
  >
  > 73 de Brian, VK2GCE.
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