[SECC] Adjusting tuners

[Tom W8JI]

> 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.

It isn't resonance Jeff and it isn't match that causes the problem. A 
setting that shows a 1:1 SWR can have terrible voltages or good voltages.

The problem is how things are tuned. You always should use maximum possible 
capacitance and minimum inductance that allows a match. That tuner's manual 
was never corrected, but later manuals were corrected to reflect this.

By the way, this applies to every T-network tuner made by any company.



 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.

Sounds like you have a lot of arcing problems with multiple pieces of gear. 
I think a lot if not all problems would go away if you followed my advice on 
how to adjust a tuner. This would apply to the Dentron you are having 
problems with, or any other tuner.

I only meant the advice to help you not have arcing problems in the future, 
and it will apply to any T network.

Again, SWR does not matter nor does "resonance". The correct way to tune a T 
network is to use the maximum possible capacitance and minimum inductance 
that allows a match. Keep the capacitors meshed as much as possible.  :-)

> I think I'm done with MFJ and will just look for another old Dentron 
> tuner,
> which seem to be built pretty good.

If you tune the Dentron the way I described, it will be much more reliable 
too. If it is tuned with a lot of inductance and little capacitance, it will 
arc too. Every T network made behaves this way no matter where it comes 
from.

A second advantage is you won't have to retune as much moving up and down 
the band in contests. The tuner will have wider SWR bandwidth, so there are 
many advantages to tuning correctly and using the most capacitance possible 
and least inductance that allows a match.

This hint works with any traditional T tuner. If they arc, they are probably 
tuned wrong no matter what the SWR is.

73 Tom