Today I took down my Cushcraft MA-5B again to investigate the problem of high SWR on 20m and 15m and after a struggle to get the traps on the driven element disassembled, this is what I found.
The bottom section was taken from the ‘hot’ side of the feed, ie the centre core of the coax and the top one was taken from the braid side. You can clearly see where the plastic coil former has got hot, melted and discoloured badly. On a close inspection it looks as though some of the windings have shorted together which would explain the symptoms. The plastic coil former really is beyond repair.
Clearly this shouldn’t happen, especially when running legal power but I’ve checked eHam and it seems to be quite a common problem.
Here’s a close up of the melted MA5B trap section.
(both these pictures are clickable for [very] high resolution versions)
I’ve already contacted Cushcraft who have demonstrated superb customer service and are sending me a replacement trap. Hopefully it won’t take long to arrive and I can be properly back on the air. I am still going ahead with ordering a Hexbeam though to replace the MA5B but I’d like to get this aerial fixed as quickly as possible.