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Author Topic: 10 Meter input coil tuning problem with AL-80B  (Read 4669 times)
K4PVA
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Posts: 0




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« on: April 04, 2012, 09:46:48 PM »

I have an Ameritron AL-80B that I bought second hand. I knew that it had an
arcing problem when I bought it so I sent it to Ameritron for repair. They
reparied it and fixed the problem (replaced the loading capacitor) and returned
it to me.

I have been adjusting the input coils  using an MFJ-259B antenna analyzer and plastic hex tools. I was able to get 1.2:1 and most of the time a 1.1:1 swr throughout 160, 80, 40, 20 and 15 meters with no problem using this technique. Was easy with repeatable readings.
Amp works great on these bands.

When I tried 10 meters on the "AUX" position it was a different matter.
Ameritron assured me that the 10 meter mod had been made. However, tuning the
slug with the plastic hex tool makes NO difference in the swr. It remains at
2.6:1 no matter how much I turn the slug in any direction.

I tuned the MFJ-259B down frequency to see where the 10 meter coil might be
resonating and the lowest swr was at 21.090 mHz (!). No amount of adjustment
would change that.

I think that either the mod was NOT made or I have a bum 10 meter input coil to
replace. Or maybe a wrong coil was installed in the first place. Any ideas or
anyone have the same problem? Greg, K4PVA.

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KA5N
Member

Posts: 4380




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« Reply #1 on: April 05, 2012, 02:56:26 AM »

Maybe a bad solder joint or connection.  While the core may turn it may not be screwing in and out of the coil.   Wrong value capacitor?   Who knows?  I would just order a new coil and
capacitors for 10 meters and see what happens.   The previous owner may have had the same
problem and kept messing with the tuning until he wore the threads off the core.  They may have accidently put a 15 meter coil in at the factory.  What happens if you try to tune the
10 meter position to 15 meters? 
Allen
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W9GB
Member

Posts: 3379




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« Reply #2 on: April 05, 2012, 10:20:19 AM »

As suggested by the answers on QRZ to your multiple-posted question,

I would first do a visual inspection (use a magnifier & good lighting) to look
for corrosion on band switch contacts, assure all steps of 10 meter mod were performed,
and wiring is correct.
It could be as simple as a missed solder connection!
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