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
> > > >
> > > >
> > > >
> >
> >
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