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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