How Old is Old?

FM does it with frequency!
Posts: 514
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: How Old is Old?

Post by Kelly » Sat Feb 11, 2017 9:03 am

As I remember, the reason they used to use watchband interconnecting bullets were supposedly the watchband segments conformed better to out of round center conductors caused by uneven extrusion of the copper. The downside is exactly what you found; the watchband develops high resistance over time as thermal cycling and any corrosion gets between copper and the band, leading to increased resistance and eventually catastrophic failure.
Skype:kellyalford Twitter: @KellyAlford

Posts: 125
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: How Old is Old?

Post by Lee_Wheeler » Sun Feb 19, 2017 11:44 pm

Barring anything strange happening I should be able to light this back up tomorrow. After drive I need to switch one of my other stations that is co-located just under the 5 bay to the aux site and then get the line purged with nitrogen. We found a cracked elbow at the top where it makes into the antenna so that had to be replaced and we have replaced all of the watchband springs top to bottom. Everything from 800 ft down was dropped out, cleaned with Scotbrite and alcohol, and reassembled with all new Teflon centering pegs and top retainers.

The top burnout was a biggie but at the top of that section there wasn't a speck of contamination. I am used to seeing smoke contamination but it looked pristine.

There were several watchband springs that were moments away from blowing which is why I went ahead and replaced them all (at $90.00 a pop - ouch).

The replacement centering pegs that I originally ordered didn't work and SWR doesn't remember that they ever made 4 1/6" line with uniform cross section 1/2" diameter centering pegs. Kudos to them though, they redesigned a suitable replacement and got them out the door overnight just in time.

The crew didn't much like the latex gloves but the line went back together untouched other than by clean clots and alcohol and it is pretty much hospital clean.

Just for fun here are some more pictures.
Burnout at Section 40.jpg
Burnout at Section 40
Burnout at the top of Section 39.jpg
Burnout at the top of Section 39.
A few springs that were ready to fail.jpg
Watchband springs that were ready to fail.
Inner Conductor before cleaning.jpg
Inner Conductor before reconditioning.
Reconditioned Inner Conductors.jpg
Reconditioned Inner Conductors.

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