> My first stop was to look at the Ameritron/MFJ/Vectronics units. After
> all, they are the most prolific tuners out there right now. Upon looking
> at all these units, I found that the plate spacing on their caps were no
> better than what my Heathkit had. Even their highest power units had caps
> with the same spacing. It is interesting to note that later I noticed
> that the Ameritron tuner rated for 1200 Watts has larger cap spacing than
> the ones that are more expensive and rated for higher power!
Well Jon, it might be advisable to spend time looking at voltages in
T network tuners. If you run the numbers, you'll see the largest
problems causing arcing are excessive Q on the low bands.
Excessive Q is caused by not having enough capacitance.
many people operate tuners incorrectly. They don't use maximum
capacitance possible when matching loads. That will make any
tuner arc or fail.
That's why better tuners for the low bands and for high power have
more plates in the capacitors, even if it means reduced spacing.
There is absolutely no reason to have the plate spacing larger than
the air gap in connectors and switches, providing you have enough
capacitance on the lowest bands. It's a design balancing act.
For example, the ATR30 will handle over six kilowatts into most
loads on 80 meters yet the wider spaced MFJ 989C tuner will arc
in the capacitors and fail at several hundred watts under the same
load conditions.
> Well, upon getting the tuner home, I immediately went to 80M, tuned up and
> VIOLA! - NO ARCING!! So, I was like, COOL! I've used the tuner on just
> about all bands now at full legal limit and it works just great. It will
> even tune my 80 m dipole on 160 m which is something my Heathkit wouldn't
> do.
>
> My only complaint about the unit is that the roller inductor is a little
> stiff and hard to turn in some spots, but that will probably get better
> over time.
Maybe. Maybe not. Look at the roller construction.
When MFJ bought Paul's last company (vectronics), I was
assigned the task of looking at the rollers to see what could be
done. Ameritron inherited roller parts from that sale. The roller used
a chrome plated bushing riding on an aluminum shaft in the roller,
and had other mechanical connection problems such as a lack of
wiping contacts to insure solid connections. There were steel wave
washers in the path of RF current, and steel on aluminum hardware
current carrying points.
Eventually all those parts were scrapped.
What materials are used in the roller contact area?
> Also, Palstar makes power meters. They have a very reasonably priced unit
> that is a 3KW unit that is a pseudo peak power reader. It is about $75.00
> or so. A much better price than similar units from MFJ/Diawa, etc who may
> not even make a 3KW meter or would charge well over $100 for it. Sure,
> it's not as good as a Bird, but it is a very nice unit.
Ameritron makes a TRUE peak reading 3 kW meter. I don't know
how much it costs, but I do know it can handle 6 kW.
73, Tom W8JI
W8JI@contesting.com
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