[ARC5] Filament Question

[Bruce Long]

Wayne  I suspect Leslie is correct or at least he convinced me.   If it was my rig I would have the filaments on all the time but I would reduce the filament the filament voltage by 10 or 20% percent during the "off" time in order to save cumulative filament emission.

      From: Leslie Smith <vk2bcu at operamail.com>
 To: ARC-5 List <arc5 at mailman.qth.net> 
 Sent: Saturday, October 3, 2015 12:53 AM
 Subject: Re: [ARC5] Filament Question
   
  Hello Wayne,
  Lacking any specific knowledge about your question, my guess would be
  a definite "yes".
  I guess that thermal cycling would reduce the life of the filaments
  and therefore the tubes.
  I suspect (from your question) you think the same as I do.

  In an editorial in "Ham Radio", the editor Jim Fisk, wrote about a
  surplus receiver he had operated from the mid-40s.
  I may be wrong in detail here, but as I recall his editorial, his set
  was wired so the filaments were always on.
  He switched the B+ line when the set wasn't in use.  He believed (as I
  recall) that the thermal cycling of metal to glass (in the tube base)
  was the main source of failure of tubes.  He pointed to the 30 year
  life of his set, with the filaments constantly on, as evidence of his
  hypothesis.

  I don't know if he's right, or not, but his theory seems to have
  reason on-side.


  73 de Les Smith
  vk2bcu at operamail.com


On Sat, Oct 3, 2015, at 12:27, Robert  Eleazer wrote:
> I have recently gotten interested in firing up my RT-70/GRC, mainly
> because I started testing the tubes in it with my tube tester in attempt
> to identify the cause of missing transmit audio.  By the way, the first
> clue I found when I took the set out of its case was a broken 3Q4.....  
> 
> The RT-70 was designed to be powered by batteries in the PRC-16 version
> and so I guess that is why the tubes are DC powered instant heating
> filaments that cycle on and off depending on transmit and receive.
> 
> Would it be better for the longevity of those tubes to rewire the
> filaments so that they are ON at all times when the set is powered up
> from the AC power supply I built for it?
> 
> Thanks,
> 
> Wayne  
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