[TowerTalk] Repairing & Bench Testing TA-33 traps

[Derek Cohn/WB0TUA]

Dear All,

With the great advice that I received from everyone the past couple months, I was able to buy a down-trodden TA-33 for a Field Day antenna.  This TA-33 had been stored outside, on the ground for about 15 years.  Since many of you on the list helped me with suggestions for evaluating the beam, I was able to determine that all the critical parts were present and that the trap forms had hairline cracks before purchasing it and didn't overpay.  Ten of the traps were white forms, one was a black form (perhaps replaced sometime in the past) and one was a brownish purple (that was a new one on me).

Today, I started working on the antenna with a fellow ham who is a mechanical engineer.  We inventoried all the parts and they seem to be there.  We took the traps apart, cleaned them up and, sure enough, all of them had hair line cracks.  We set those aside for the moment.  We then put all the aluminum elements in the lathe, spun them around and used fine steel wool to remove the corrosion.  We also did the trap covers and everything looks good so far.  

Next weekend, we're going to tackle the traps.  The friend who is helping me on this has a full machine shop and is suggesting that we put the trap forms in the vacuum impregnator he has and fill the cracks with epoxy.  He's concerned that even if we assemble the beam and it tunes up with an antenna analyzer, the cracks might cause the coils to break down when we use our 100w transmitters on Field Day.  We do not intend to use amplifiers.

If this antenna were going to be a permanent installation, I wouldn't fool with these traps and would just replace them with new stock from Mosley.  However, since I don't anticipate using this beam more than one weekend a year (Field Day), I don't want to sink all that money into it if I don't have to (I think the trap set is about $260.00 from Mosley).  So...now to my questions:

* Anyone see any problem with us vacuum impregnating the forms with epoxy.  Is there a "preferred" filler for this?

* Can someone recommend a test procedure for evaluating the integrity of the traps on a bench before we assemble the antenna?  My friend has a wide array of test equipment available but I'm not sure of an appropriate test procedure.

I took lots of pictures today of us cleaning up the beam and hope to put together a web page as the project progresses so everyone can benefit from what I've learned from you guys.

Thanks for any help you can give me!

73,

Derek Cohn
Morse Telegraph Club - Alton Chapter
Office UD, Sine DJ
Amateur Radio Station - WBØTUA
1969 Brunswick M274A5 Mechanical Mule