Thanks Tom.
I don't understand what happened because I have the settings for each of the
bands marked on the tuner. So it wasn't way out of resonance when this
happened. In fact it had a perfect match on 20 meters and for no reason the
ALC on the radio started jumping around and shortly after that it started
arching at the switch for choosing the inductances. The contacts are fried
and the switch probably would have to be totally replaced. It is out of
warranty so I just chucked it. I owned at least two other MFJ 901B's in the
past and both of these expired with arching issues as well. I doubt I would
buy another one. I have also fixed several of K4BAI's MFJ tuners that have
had issues with poor connections in the past.
I think I'm done with MFJ and will just look for another old Dentron tuner,
which seem to be built pretty good.
73, Jeff
-----Original Message-----
From: secc-bounces at contesting.com [mailto:secc-bounces at contesting.com] On
Behalf Of Tom W8JI
Sent: Sunday, September 19, 2010 10:03 PM
To: secc at contesting.com
Subject: [SECC] Adjusting tuners
> on the 756PRO. I need to buy a new headset with the Icom 'IC' element in
> it.
> About 20 mins in I notice a burning smell. My MFJ 901B tuner is arching
> over
> on the switch that is used to switch in the different inductances. I
> opened
> it up and it was totally fried. (running just 100 watts.. what junk !!)
Here are some very simple useful tips for anyone using a conventional T
network tuner:
There are a nearly infinite combination of settings that can produce a
match.
When you adjust any T network tuner, try to always start with maximum
capacitance. Always use the maximum possible capacitance, and minimum
possible inductance, that allows a match.
If the user somehow manages to use very low capacitance, voltage inside any
tuner can become very high even at very low power. A tuner that can handle
600 watts when properly tuned can fail at 60 watts when mistuned.
Learning how to adjust a tuner will greatly extend the life of any tuner. We
need to remember is one thing....use maximum possible capacitance and
minimum inductance that allows a match.
> figured I would just stop and go ahead and make the repairs to my Dentron
> Super Tuner that I bought parts for in Huntsville.
When repaired, adjust the Dentron as suggested above and it may never need
repair again! Always remember one simple rule.... minimum inductance and
maximum capacitance that allows a match.
73 Tom
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