Tuners
> Anyone out there using a MFJ 969....effect appears to be deminished by
> the roller inductor....I get great SWR's for a change....like 1:1 but I
> dont get the same feeling from the system.....am attempting different
> directions on the roller inductor.....
Jim reported a while back that it is less effective. I don't
know why, but it does illustrate how lower SWRs don't necessarily
mean a better wave. I would think, though, that the
tuner with the internal balun would be more effective or
at least efficient, but again Jim reports the 949 with 912
produces a better wave.
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I am having trouble with my 969 roller inductor overheating, as
a result of the conductive grease hardening on the brass shaft
on which the roller advances along the helix of the coil, I
have in my possession a Type 19 ex WW2 transceiver, and it has
an excellant inductor, switched with a very H/D 10 Pos switch.
Am going to adapt it in place of the roller inductor. Will keep
you posted.
John in Australia
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>From hastbrak@nor.com.au Fri May 29 07:01:28 1998
Hallelujah! Those on the list may recall some probelems I was
having with my tuner, particularly the roller inductor, well I
fixed it!!
I removed the roller inductor, and made up a 2 turn coil - 2
inches in dia out of 16 gauge tinned copper wire, and a friend
supplied me with a 12 position switch. I tapped the coil
(inductor) at 30 deg increments & connected this to the switch,
and voila!! low VSWR, and no more problems. Anyone want a MFJ
roller inductor??? I found that the inductor switch position is
in the 3 rd position from the start of the inductor, so anyone
wanting to make up a switchable inductor, you only need to put
in a maximun of 6 positions.
This problem has been bugging me for some time, and now it's
fixed - yippee. Now for some seroius Rifing
John in Australia
=====================
Those on the list may recall some problems I was having with my tuner,
>particularly the roller inductor, well I fixed it!!
<snip>
>connected this to the switch, and voila!! low VSWR, and no more problems.
<snip>
Inability to obtain a low VSWR reading with a tuner is often caused
by inadequate design of the tuner, which usually manifests itself at the
upper end of the tuning range. Of course, that happens to be exactly
where we need it to work. <G>
Usually the culprit is that the coil has an unwanted resonance due to
coupling to other wiring in the tuner enclosure, or the leads connecting
the coil to the circuitry is poorly placed or too long. Often times,
the manufacturer, in an effort to make a less expensive unit, will jam
the parts into too small a case, causing a loss of efficiency and
unwanted interaction between components at various frequencies.
I've built many antenna tuners over the years, including some
commercial units for broadcast stations, and the first rule in building
one was to make the box big enough to space the tuning components far
enough apart so they don't interact in unexpected ways.
Adding a fixed coil removes many of the interaction problems, with
the trade-off of causing the unit to be unable to operate on other
frequencies away from 27.12 mHz. That, of course, is probably not a
problem for most of us.
I've often thought about designing a tuner specifically for Rife/Bare
work - dunno' what the cost would be though, I'll have to see what I can
locate from suppliers.
Ralph W5JGV
========================
I finally got to test one of Don Tunney's new RB300A antenna
tuners. All I have to say is that it completely blows away any
other tuner I have tested.
Every part of the tuner is first rate and of the highest
quality. Unlike competing tuners from MFJ,the RB300A tuner has
no plastic parts that will melt, there are no contact switches
to burn, no poorly done wiring. This is a first class piece of
construction that returns outstanding SWR's with every tube
I've tried it on.
There is a fixed inductor and a built in 912 size balun. All
one does is set the SWR by adjusting two tuning capacitors over
a very narrow range.
The RB300A will handle up to 300 watts and is designed
specifically for use with R/B devices. Even the cover has a
nice logo on it that says "Rife Technology - RB300A Resonant
Light Wave Plasma Tuner "
If anyone is thinking of buying another tuner, this unit is a
must. Talk to Don about his tuner, price is comparable or less
than the MFJ's with a 912 balun.
Dtunney@mars.ark.com 250-338-4949
Jim Bare
=======================
I just recieved a new MFJ 948 tuner. This is essentally the
same as the 949, but lacks a dummy load. Taking the cover off
of it, I found that the inductor has been radically modified.
The inductor is now variable in multiple substeps, and is wound
on a small ceramic form.
Fired up a tube with the tuner and everything worked fine. Then
at about 5 minutes the power to the tube started to drop.
Pretty soon the tube looked like it was getting only about 40
watts to it, but the power meter on the tuner was saying 250
watts. The SWR started to drop and the tube kept getting dimmer.
Turned off unit and checked the tuner. Seems that new inductor
starts to act as some sort of dummy load as it gets hot. When I
checked it, it was incredibly hot after soaking up 250 watts
for about 4 minutes.
Got some big problems here, I don't know if the new 949's are
being made with the same inductor, but if so, they are now
essentially worthless to us.
I figure I can fix this by winding up my own inductor, but why
should anyone have to do this?
Be carefull if buying a new tuner and try and get one from Don
Tunney to be on the safe side.
Jim Bare
=====================================
I finally got my 948 MFJ tuner working. I tried a variety of
fixes and finally settled on one used by John Trenning in
Australia.
I did try to salvage the ceramic inductor by hard wiring it
into the L position and fixing a rather nasty kink MFJ puts in
the inductor wire to keep it locked into the inductor. This
did help, got to about 15 minutes this time before it started
adsorbing all the power.
John's fix is relatively simple.
Remove the Ceramic inductor. You must take the adjustment knob
off the front of the chassis with an allen wrench, unscrew the
mount from the chassis, and unsolder the wire that goes to one
of the tuning capacitors.
Make an inductor coil of buss wire. The coil is 4 to 5 turns,
2" diameter, about as high as the capacitror solder eyelet it
will attach to. Attach one end to the chassis, attach the other
end to the capacitor where the ceramic inductor was soldered.
Take another piece of buss wire about 4 to 5" in length and
attach one end to the chassis. Attach the other end to the top
coil of the new inductor coil very near where the wire comes
off the coil and stretches over to the capacitor. Do not attach
the wire to the capacitor, this will not work. It must be
attached to a point over the body of the coil. You can try
moving the attachment point back and forth a bit to minimize
SWR readings. Again on the top coil.
I solder small eyelets onto the ends of the wires that are
attached to the chassis and use a nut and screw to hold them in
place. A spare screw and nut from the Speaker mount of a Uniden
510 works great.
So far so good with the fix.
Jim Bare
====================