Bill,
Your right, I did forget the RM Italy amps. I personally wouldn't recommend
one, theyr'e pure junk. They use self tapping screws to hold the RF transistors
down. What happens is when they run them it, it puckers up the aluminum
heatsink around them and lifts the transistor up off the sink! There fix was
just to try and glob on a bunch of heatsink compound. After the heat has time
to dry the compound, the transistors finally burn out. The only way to cure
that afterwards is try to use a large flat file and bring the surface down back
even. The best fix is take the heatsink and have it milled flat, and re-tap the
holes.
Next, the pc boards they use are the cheapest they can get. Theyr'e made of the
old yellow paper type phenolic and the glue that holds the copper foil down is
weak. To compound the problem, a lot of the traces are not wide enough for the
current they carry. When a component goes out, it generally burns the trace off
completely at the part. Then the rest of the trace curls back off the board an
inch or so. To make matters even worse, the soldering is very poor. The people
they hace soldering them up leave cold solder joints all over the place. I know
of dealers who bought them new and the very first thing they did was go over
all the solder joints.
This holds true on their base amps and other products. The meters in the front
are held in with that old rubbery horse shoe glue, no brackets or screws here.
They made one amateur amp that they called a 2000 which only had two 572B's in
it. They tried to switch the tank coil connections around with relays instead
of a RF duty rotary switch. Compound that with all the above problems. I know
of a few bought here in the US and after the word got out, the dealer got stuck
with a bunch of them and practically had to give them away in the end. The
transformers in them is something else. Theyr'e about 1/3 less in size than
what they ought to be iron wise.
Speaking of the dealer. The two who brought those into the US to start with was
Copper Electronics, and H&Y Electronics (Father & Son team) down in Louisville,
Ky. I heard the FCC busted them again about a year back. I also know they dont
have any product around their offices in Louisville, and warehouse everything
across the Ohio River in New Albany, Indianna. So I doubt the FCC did very much
at all since they're still pumping them out. Maybe the FCC will smarten up and
read this post...cough. Maybe too they'll look into what I heard about Midland
owning RM Italy and Zetagi.
Another I left out is the Texas Star amps. Theyr'e almost as cheap and wired
together in modules of two transistor sets with 40 acres of wire. They use push
button controls which are real bad to go out. The RF transformers and combiners
are way undersized. Steer clear of these too.
Ok, I'm done. I don't think I really left out any more.
Best,
Will
----- Original Message -----
From: K4IBC <k4ibc@bellsouth.net>
To: "Will Matney" <craxd@engineer.com>, Amps@contesting.com
Subject: Re: [Amps] Mobile amps
Date: Fri, 22 Jul 2005 16:10:10 -0400
>
> While I noticed you didn't mention a certain brand that appears often
> forsale. What about those made in Italy ? It maybe a sore subject I don't
> know?
> Bill
> K4IBC
> ----- Original Message -----
> From: "Will Matney" <craxd@engineer.com>
> To: <Amps@contesting.com>
> Sent: Friday, July 22, 2005 1:56 PM
> Subject: Re: [Amps] Mobile amps
>
>
> > Carl,
> >
> > They're pretty much all the same, or the ones that use dead bug
> construction except for a few. There is the following brands I know of that
> I've seen the innards of that were ok to convert. Below are a few;
> >
> > X-Force
> > Davemade
> > Fatboy
> > Skywalker
> > Joker
> > Armadillo
> >
> > The Snowcap Technologies brand is junk I think as they make a realy flimsy
> cabinet out of what looks to be aluminum gutter flashing. It's pretty rough.
> There's another named Big Dawg which always had a pretty bad rep but I've
> not seen one up close to really say. There's other brands too I couldn't
> comment on because I've never seen under the hood.
> >
> > For ones with printed boards, those Palomar brand knockoffs are ok but
> they're bias is unconnected at the factory. They still sell them saying
> they're class AB1 but when you look, they're class C. They tried to just use
> a series resistor and a clamp diode for bias and evidently their design
> wouldn't work. Which all the others besides Joker did that type of bias
> circuit too. The Palomar knockoffs also have a double sided pc board and the
> through connections are bad to break as the soldering isn't great.
> >
> > First thing is to rip out all the wire they generally have strung all over
> Gods creation and re-wire it correctly. Get rid of the rats nest keying
> circuit they're using, and put one in that is correct for the use. Lift the
> ground on the input transformers and connect the bias. Add feedback if it
> dont have it as some dont. Add an attenuator for amateur transceivers. Add a
> tuned output if it dont have it and place a good low pass filter behind it.
> If used over the whole amateur band, add a good bandswitching circuit. This
> would be the minimum. You can add safety circuitry to trip out on a high
> SWR. Over current protections, etc. which is the bells and whistles. It's
> all according to how much you want to spend and modify one.
> >
> > >
> > > Hi
> > >
> > > Do you have any amps you would recommend for this project?
> > >
> > > Carl
> > > N8CDW
> > >
> > >
> > > ----- Original Message -----
> > > From: Will Matney <craxd@engineer.com>
> > > Date: Friday, July 22, 2005 9:27 am
> > > Subject: Re: [Amps] Mobile amps
> > >
> > > > Dan,
> > > >
> > > > Yes, they are really the same wide-banded amps that have been
> > > > around for years and the same as in the Motorola app notes. Most
> > > > use the 2SC2879 transistors. The only thing is for them to be
> > > > linear, and clean, they have to be converted to class AB1 or AB,
> > > > an output filter should be used, and a bandswitching network
> > > > added to the input to level the SWR across the bandspread.
> > > > Generally these are made by the one doing the conversion as
> > > > there's too many differences in amps to make a one-size-fits-all
> > > > type of circuit. They generally make them using switchable pi net
> > > > circuts switched in with relays from a rotary switch on the front
> > > > of the amp. Henry did this on their mobile amps and is the upper
> > > > board over the main one. These 11 meter amps dont have this. What
> > > > I'm making is a good RF keyer, and the bias circuit to set the
> > > > transistors to class AB, or AB1. The keying circuit they've been
> > > > using on a bunch of different models just tie the parts together
> > > > in mid air, and look like a rats ne
> > > > st. Terrible construction, but the rest of the amp is usable.
> > > > Another thing that will have to be used is an attenuated input as
> > > > 5-20 watts will open up a set of 2SC2879's to their rated output.
> > > > That is if the transceiver can't be cut back. However an
> > > > attenuator is easy to build. You can buy these amps second hand
> > > > off eBay for a good bit less than new. I may even build some new
> > > > ones but that's a good bit in the future. For homebrewers, I can
> > > > get the cabinets, and heatsink along with other parts they may
> > > > need. There is also pre-punched PC boards but not etched. The
> > > > punched holes are for the transistors. These holes can be made
> > > > though by drilling the board first, and then cleaning up the rest
> > > > using a spiral bit in a mini-router, or a Dremel tool with a
> > > > router base added. The best drill to use is one of those cone
> > > > bits. The way they've been building them is by dead bug
> > > > construction. I prefer to use an etched board myself, but do use
> > > > surface mount with through hole components by bending the leads.
> > > > Those amps are too hard to repair without the parts mounted on
> > > > the top, and unsoldered from the top. Those traces can be routed
> > > > too if you have a steady enough hand. Hope this helps.
> > > >
> > > > Best,
> > > >
> > > > Will
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Dan Sawyer" <dansawyer@earthlink.net>
> > > > To: "Will Matney" <craxd@engineer.com>
> > > > Subject: Re: [Amps] Mobile amps
> > > > Date: Fri, 22 Jul 2005 06:59:46 -0700
> > > >
> > > > > > Will,
> > > > > > Is it practical to adapt these to work on 80 through 10 meters?
> > > > > > Thanks,
> > > > > Dan
> > > > > > Will Matney wrote:
> > > > > > > All,
> > > > > >
> > > > > > Some have been buying those 11 meter mobile amps and
> > > > converting > > them over for amateur use. The ones which use
> > > > un-etched PC > > boards, etc. The RF keying in these are
> > > > generally rats nests and > > pretty weak circuit wise. Most dont
> > > > last very long and are for > > use only with about 5 watts max
> > > > input and have no SSB > > capabilities. I am now offering
> > > > retrofit kits for RF keying, and > > bias control. Most are made
> > > > class C only and the ones with any > > bias are not adjustable
> > > > only using a diode clamp. I can do these > > on tie strips or on
> > > > small PC boards made to mount upright on > > edge. The tie strips
> > > > take up the less room. If any are interested > > in these, give
> > > > me an e-mail. I'll be glad to help in converting > > these in any
> > > > way possible.
> > > > > >
> > > > > > Best,
> > > > > >
> > > > > > Will
> > > > > >
> > > > > > Amateur Transformer & Supply
> > > > > >
> > > > > >
> > > > > >
> > > >
> > > >
> > > > -- ___________________________________________________________
> > > > Sign-up for Ads Free at Mail.com
> > > > http://promo.mail.com/adsfreejump.htm
> > > >
> > > > _______________________________________________
> > > > Amps mailing list
> > > > Amps@contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/amps
> > > >
> >
> >
> > -- ___________________________________________________________
> > Sign-up for Ads Free at Mail.com
> > http://promo.mail.com/adsfreejump.htm
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
--
___________________________________________________________
Sign-up for Ads Free at Mail.com
http://promo.mail.com/adsfreejump.htm
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|