[Elecraft] cold flow

[Charles Harpole]

Cold flow is an interesting factor hams must know about.  Many plastics and things with placastizers in them (I failed 7th grade spelling) will

change shape over time when put under pressure.  The inner isulation of coax is a major item... when coax is bent, the inner insulator (and the outer one also)

changes shape.... the more sharp the bend and the longer it is bent the greater the cold flow changes.  Tell that to the cable guy who routinely puts coax in 

90degree bends and staples them tightly into that shape.  

9913 is particularly at risk due to its spiral plastic string inside.  Some coax data charts will tell u the max sharpness bend a specific coax will stand up to.  

Of course, cold flow applies to vy many other items.   73


Charles Harpole
k4vud at hotmail.com






> From: darjar at comcast.net
> To: ng3v at comcast.net
> Date: Thu, 22 May 2008 08:22:06 -0400
> CC: elecraft at mailman.qth.net
> Subject: [Elecraft] KPA100
>
> Tom,
> The reason for retightening the screws on the KPA Power Transistors is Elecraft uses plastic insulating heatsink pads. They tend to cold flow a bit under pressure.
>
> Because of the above you should retighten the screws about 2 to 3 days after you first installed them. Operating time is not a factor.
>
> 73
> Dave KD1NA
>
> -Hello group,
>
> -I built the 100 watt amp last summer, but can't seem to overcome the urge to
> stay at qrp levels.
>
> -So, as I probably have only a few minutes of time at 100 watts, when should
> I reset the mounting screws. Is this like 3 months or 3000 miles or is it
> strictly a matter of time?
>
> -Should I just pound out a few hours of tests into a dummy?
>
> -Thanks,
>
>
> -Tom
>
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