[Milsurplus] Fw: Who is GHS?

[Bruce Gentry]

There were many pieces of gear from that era that ran blazing hot.  In 
the case of the SRR_____  series, omitting the screen resistors may have 
been for economy and/or "reliability", eliminating the screen resistors 
and bypass condensers left fewer parts to fail. Tubes were expected to 
wear  out, so replacing them when weak  was probably not counted in 
reliabily figures unless they failed catastropically.  ARC-27s, and 
GRA-53s/TRC-68s were two I knew well that cooked themselves to death, 
and a lot of the radio relay gear of the same era did too. Many of the 
sub miniature tubes were run as hard as 7 or 9 pin miniatures, without 
the large envelope and structure to dissipate the heat, and a lot more 
of them were crammed into a very small space. I also think many 
manufacturers knew transistors were on the way,  tried to miniaturize 
tubes so their gear would not look so obsolete,  and stave off the costs 
and effort to change to solid state as long as they could.  Does anyone 
know of any military rigs that used Nuvistors or Compactrons?  Those 
were other efforts to hold off the inevitable.


        Bruce Gentry, KA2IVY



On 10/3/18 2:49 PM, Kenneth G. Gordon wrote:
> On 3 Oct 2018 at 14:19, Jim Whartenby wrote:
>
>> As with the ARC-21, subminiature tube reliability was dismal.
>
>
> In that rig, many of the tubes are run very hot and this contributed to short life in that series
> of receivers.
>
> Yet if those tubes are used at or below their maximum ratings, they are very reliable.
>
>
>
> At first, we had a lot of failures, but after I modified them so that the screen voltages to the
> pentode/tetrodes was reduced to "somewhat below" the plate voltage (!), temperature
> dropped markedly, operation appeared normal, and the receivers then became much more
> reliable.
>
> As I remember it, the screens were essentially connected directly to the plate supply. I
> added suitably bypassed 51K resistors to the screen feed at all those tubes which required
> it and that made a big difference.
>
> Ken W7EKB
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