On 2/3/2014 1:19 PM, Tom Osborne wrote:
HI All
I purchased a MFJ-898C roller inductor tuner that I got for a really
good price. It had a problem that it took a while to figure out.
This was discussed on the Amps reflector in just the past couple of weeks.
One thing brought up was the need for preventive maintenance (cleaning
the coil and contacts as they can and often do get dirty. If used with
low impedance loads they are derated (all tuners are derated for low
impedance loads AFAIK) the wire in the 989 series is pretty small for
the legal limit into low impedance loads. I used a pair of them for
some years and with cleaning the rotary coil periodically they worked
fine. I've forgotten what they were derated to on 160 with a 35 ohm
load, but think it was 500 or 800 watts.
On 160 I had to raise the resonant frequency of the antenna to near the
top end of the band or they'd arc. No damage, just a hiss like cat,
snake, or a leaky tire. That did cause some concern about the current
at the low end of the band, so I now have an AT5K and an AT5K HP
Your point about cleaning the coil and contact is a good one and should
apply to most tuners with rotary inductors.
73
Roger (K8RI)
It would tune an antenna at low power fine, but at high power, the SWR
would slowly creep up and not stay tuned right. I tried all sorts of
things to fix it like spraying the contacts with cleaner, etc.
Yesterday I happened to notice the roller inside the coil that
contacts the coil wire looked black and dirty. I sprayed it with
contact cleaner and took a real small screwdriver and cleaned the slot
in the roller where it contacts to the coil.
After cleaning it, it now works like it should and the SWR stays put,
even at high power with no arcing, etc.
Posted this because maybe someone else is having the same problem
No comments about MFJ stuff needed - I've heard 'em all :-) 73
Tom W7WHY
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