Antenna Trap problems

[AB3FL]

I have a Mosley TA-33.  I recently acquired the TA-40KR kit to extend it to operate on 40M.  It worked fine for a day or two then I starting having issues on 20M and 40M.  I took the antenna down today and see that the traps zorched on the end toward the feedpoint.  What would be the best way to repair these and how do I get rid of ALL of the carbon tracks?  Mosley wants an arm, leg, and n#t for each trap.  I have tried with a hot glue gun which did work on one trap, but I think there is still a carbon problem.  I repaired it and it was able to hold 150W from my TS-950SD, but as soon as I turn on the maul and only give it 400W after a few seconds the SWR skyrockets. 

thanks

Tom - AB3FL

Hope to find you on 40M yA-eM once I get this fixed

[W7TFO]

The cause may be either moisture, or harmonic content in your RF.  OTOH, the ends may be set too short, causing the impedance to look capacitive and have too much reactive voltage at that loading coil.

To fix, the only way is to dig out all the corrupted plastic (carbon), and rebuild it with something with high dielectric strength, maybe premium epoxy.

There is obviously a high voltage node at work there.  A sweep at the op freq is in order.

73DG

[flintstone mop]

Dumb Question::::: Was this optional add-on installed according to Mosley? Measured properly??
Or stuck on and adjusted using the MFJ 259?

The trap looks like good quality stuff.

Fred

[Jim, W5JO]

Have you removed the ends of the trap to see what the deal is inside?  Pull that black cover back and there is a screw that once removed will allow you to pull out the end of the trap for inspection.  You should find the coil wound on a high quality teflon form.  Be sure those forms are not broken in any place.  Once you do that, it will be easy to reassemble and very evident how the work.  I have a TA 53 that suffered the same problem and it turned out both traps on the 20/15/10 meter element were blown slightly apart inside.  That caused similar problems as you have.  I tried Q dope on mine after cleaning and attempting to get the coil back into original shape and didn't have any luck.  That 40 meter kit is Mosley design and the tube that is inserted in the end of the 20 meter element has holes for the upper and lower part of the band.  Did you use the right hole for the end of the band where you wish to operate.  If you set it for the upper and then use a tuner to operate on the lower part of the band you can burn those traps with high power.  Have you had any storms around lately that could have generated a near-by strike or induced a lot of current by induction?  Sorry for the single paragraph but this board doesn't like my browser and I can't write very many lines without problems.

[AB3FL]

The traps were cracked and zorched.  I was able to order new trap coils from Mosley for about $60. 

It was installed according to the instructions from Mosley and I was testing it at the lowest SWR point.  The traps were just old and cracked so the dielectric strength was not there.

thanks

Tom - AB3FL

[Jim, W5JO]

I would almost place money it was a nearby lightning strike that did it.  Those things are well built of quality products and can stand a lot of power.  I had to replace 3 on my beam which cost me about 35% of the new antenna price.  If I had to replace all traps the cost of just the traps would have exceeded the cost of a new beam.

Glad you found the problem.

[flintstone mop]

It seems like many of these tribander type yagis turn to crap when 40M is added on.
My A3S is not what she used to be since the 40M add-on.
Measure on the ground what part of the band you want and throw her up and be done with it.

I probably would have been better off to just get a 40M rotatable dipole and mount it above the tribander separated by 10 feet. OR perpendicular to the tribander elements. I did the same thing with an A3S and the 12/17M-- 3 -element and they never 'saw each other' on the same mast.
Fred

[KA2QFX]

Just for curiosity, were you on 20 meters when the traps fried?  I ask because it looks like corona discharge did you in.

Mark

[flintstone mop]

The traps were cracked and zorched.  I was able to order new trap coils from Mosley for about $60. 

It was installed according to the instructions from Mosley and I was testing it at the lowest SWR point.  The traps were just old and cracked so the dielectric strength was not there.

thanks

Tom - AB3FL

From this post I am quoting and your first post. Did this sudden jump in VSWR and arcing continue after the replacement traps??
It could very well be  a runaway amplifier and harmonics doing the damage and not a problem in the antenna.

Fred

[Jim, W5JO]

Since this exchange I have discovered a couple of thing about the Mosley traps.  For one thing they will wind and sell the inserts that are broken so you do not need to order the complete trap.  Just tell them what antenna you have and which end of what trap and they will sell the insert that is broken.  That will save several dollars.

Second if you wish to repair them, you might try this.  Get a heat source big enough to heat the insert, I used a big heat gun.  The coil form is on that aluminum tube quite tight.  Heat the end where the wire exits the trap until it is very warm.  Place the opposite end that has the coil riveted to the aluminum tube down on concrete or strong surface.  Then use a mallet or ball peen hammer to carefully drive the free end of the coil back into place.

I am going to use some sort of glue around the aluminum tube on the free end to, hopefully, hold it in place and keep the coil form from separating.