[TowerTalk] Re:MFJ Good Stuff
K7GCO@aol.com
K7GCO@aol.com
Fri, 4 May 2001 08:03:35 EDT
In a message dated 5/3/01 4:51:28 PM Pacific Daylight Time, wy6k@yahoo.com
writes:<<
Maybe we need to start a "Why I hate MFJ" reflector!
I would, of course, be one of the first subscribers.
However, I like my AL80B (which I bought before it was
an MFJ item)>
Mike wy6k
--- "J. Leon Pringle, Jr and Audrey S. Pringle"
<w5na@megagate.com> wrote:
> N0AH:
>
> I wouldn't classify your post as a positive one! In
> fact you go out of your way in your biographical sketch
on QRZ.COM to express your displeasure with MFJ.
>
> Sounds like the kettle is calling the pot black.
> Tower talk is too nice a forum to have this type of
> posts. Why not stick to a technical discussion and let
> things fall where they may and people form their own opinions?
>
> Peace.
> 73, J. Leon Prngle, Jr W 5 North America
> ----- Original Message -----
> From: <Dinsterdog@aol.com>
> To: <kaiserdr@yahoo.com>; <towertalk@contesting.com>
> Sent: Thursday, May 03, 2001 9:48 AM
> Subject: Re: [TowerTalk] Sorry I tied up your forum,
> I'm GONE
>
> > Dave,
> Do some research on those with the most to say
> about something in a negative way and you'll find that
this little core group of TT junkies are either MFJ
> stock holders and/or sub contracted MFJ equipment
> designers-So what do they know- Stick around man!
> >
> > 73 Paul N0AH
I have something +positive+ to say about the MFJ AL80B. It's a "great
linear." It has a high efficiency final, a great ALC in the grid circuit and
a very clever Bias circuit.
The ALC is really a high level compression circuit in the final with excess
drive. As a rule more compression can be created in the final for the same
relative distortion than with the usual low level compression after the mike.
Low level compression requires all kinds of filtering and what ever gets
through is equally amplified. What ever distortion is created in a final by
the ALC compression action is only reproduced and not amplified for all
practical purposes. If an older rig like the Collins S-Line doesn't have a
compressor, some extra compression punch can be added from the final. I'd
like to see what the overall combined affect is driving the AL80B with a
modern rig with a good compressor and all that audio massaging of the
FT-1000MP and IC-756Pro. Would you believe I'll give them audio burns off
their audio gain control and RF burns off their RF gain control.
In 1953 when I was W0LMB (and still have the call) I developed an audio
circuit used in W0AJL Walt Nettles Collins KW-1 which was the first high
level AM modulation system without the conventional modulation transformer
(beside the Dohrety System). It was written up in 8/56 QST called "Single
Ended Push Pull AM Modulator. It got some play in QST about 5 years ago. It
was patterned after a 1 watt audio amp for Lab or any work flat to 100,000
cps without an output transformer developed by General Radio. Adapted to a 1
KW final it's AM audio reproduction was beautiful. Audio swings above 100
percent or below 0 percent were not possible with this circuitry. If audio
drive tried to exceed these limits, it squared off. To clean this up a
conventional pi section filter of the day was used in the HV lead to the
final. We found some "real heavy clean audio" could be created in the final
for the least distortion. The low level Speech Clipper in the KW-1 didn't
compare in any way. There are other examples of high level audio massaging I
know of that work just great.
Now the AL80B Bias circuit is very clever. It cuts the idling current to
zero when the power output is less than 100MW. This is great on stand by
eliminating all that wasted heat and electricity. W7WJP says the final tubes
runs cool as a cucumber and his Henry Amp with 2 of these tubes runs him out
of the shack in the summer. This should be the new version of the
"California Kilowatt" to help reduce the likely hood of more blackouts. I've
heard this Bias circuit is available for use on any linear for about $75 from
MFJ. I still have my old Pr 813s final from way back and will add it to this
final.
The AL80B is a great linear for the money and will be selling my 30L1 to get
one. Now if they could just add 6M to it. Or make a 50,144,450 linear of
the same design using a pr 4CX250's or 4CX300's or a pr 4CX1500's. When I
get time in the long winter months maybe I'll build it. From the Surplus
Market there is an 8x8" board with 4-4CX300's on it that would be a great
tube set up for 50-450MHz. I have this and want to know if anyone knows
where this came from and have the circuitry. Please let me know if you have
this info.
There is a great circuit in 3/66 CQ on the G2DAF Linear Amp that has a
voltage doubler in the grid circuit creating pulsating DC for the screen. No
drive, no screen volatge. I used it on the KW-1 final I have. There is
another article in CQ called "Class C Linear." The claim is it gives class B
linearity with Class C efficiency. I've used this and similar circuits and I
have no quarrel with it. Different things happen with screen voltages that
follow the amplitude of the grid drive and there is no fixed grid bias.
MFJ does have some good stuff. Martin Ju's Audio Massaging Amp is great for
"Retirement SSB Ears." The 259 SWR Analyzer is the "most useful antenna test
instrument" there is. I added Velcro straps to the case so I can attach it
to the boom or mast for hands free operation. Glue a rubber sheet to the
bottom of the case to prevent slipping. I added an external rechargeable 12V
battery to it also.
The "External Ground Circuit" worked just fine also. I'd like a chance to
improve some of their tuners, however. I've had some problems with them.
k7gco
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