On Wed, 20 Sep 2006 15:00:51 GMT, james wrote
in :

On Tue, 19 Sep 2006 14:31:52 -0700, Frank Gilliland
wrote:

+++
+++Enough of that cheap one-board crap..... this amp is MODULAR!
+++
+++Modular design allows easy repair and modification, as well as ease of
+++construction and interchangeability between different amps. It also
+++allows seperation of functions both electronically and physically. The
+++modules include:
+++
+++* Input module. Includes variable attenuator and dummy load which
+++provides adjustment of input power without 'tweaking' anything inside
+++the radio.
+++
*************

An attenuator on the input is nice. I am not sure a variable one is
needed. By variable a multistep attenuator with four to six different
values of attenuation would be a sufficient. A capability to switch
the input drive to a internal du mmy load would nice luxury item but
not necessary.


There are two reasons for a variable attenuator. First, it allows the
user to adjust the input power to achieve the best output power for
the transistors being used. Second, the circuit is physically smaller
than a stepped attenuator. The dummy load can also be external if the
driver is more than a few watts.


+++* Control module. Board that controls keying, bias & cooling fan.
+++
+++* Sensor module. Board with circuits that take measurements from
+++various locations throughout the amp and sends them to a meter. Meter
+++function selection can be by rotory switch or by LCD display simply by
+++swapping the board (module). Meter functions may include:
+++
*****************

Man talk about monitoring circuits. Nice thing to have on a high tier
amp. In reality most of these are great for development and early
testing. Actual production would cause product cost to sky rocket.


The idea here is to show all the possibilities, not necessarily to
include all of them. Regardless, a sensor module could be built that
-does- include all of them. And the rest of the amp will be designed
with numerous test points that can easily be tapped for use by the
sensor module, or just used for occasional service and calibration.
There is one major advantage of having lots of measurements available
at the front panel: it provides an opportunity for non-technical users
to learn more about the internal operation of the amp, and therefore
the best way to use it. So it could be a great educational tool for a
classroom, or maybe even a ham.


snip
+++* Power Amplifier Module. The module will consist of the amplifier
+++circuit, heat sink and cooling fan, constructed inside an enclosed
+++sub-chassis designed for forced-air cooling. Flying in the face of
+++convention, the power amplifier circuit will -not- be mounted on a PC
+++board. Instead, the components will be chassis-wired with heavy-guage
+++copper, except for the transistors which will be wired with strips of
+++copper sheet having rounded edges and corners. This allows easy repair
+++and modification, as well as more secure and robust connections.
+++Circuit will be an ultra-linear, broadband, AB push-pull design
+++(details at a later date).
+++
****************

AIr dielectric striplines are nice for the power transistors. They do
introduce some memchanical issues.


Aint teflon great? It's almost too easy to drill a small hole in the
strip and mount a teflon standoff. Heck of a lot easier than trying to
design a board around the mounting feet. And strips allow a mechanical
connection to the flags that's better than filling the gap between the
flag and trace with solder.


Great if you are in the 2KW or more
output range. In the 100 to 250 watt range 2 ounce copper laminate
would be quite sufficient.


True, if you expect the transistors to never be replaced. But that's
not the reality with CB amps. The owners like to swap transistors for
more power. Either that, or they overdrive the transistors and blow
them up. Replacing them tears up the board, which is why it's hard to
find an old single-board amp with good traces. Point-to-point wiring
eliminates this problem because both the transistors -and- the strips
can be replaced. The servicable life of the amp is almost indefinite
irrespective of the amount of work done to it.


snip
If you really want to
go whole hog on the striplines then why not take the copper strips and
either silver or gold plate them.


Because it wouldn't last, and that's contrary to the concept behind
the amp.


Word of caution on gold over copper.
Nickel is not a good conductor of RF. Nickel is usually plated onto
copper to give gold a hard surface to plate to. Plating gold directly
onto copper requires a much thicker plating so that the copper will
not leach through the gold.


Gold plating onto copper or brass is best done on top of a layer or
two of silver. You can verify this with a call to your local trombone
repair shop.


snip
*********************

Man after designing such a high tier amp, you adjust the bias through
a panel hole with a screwdriver? Will you supply the gold plated
screwdriver?


It's not "high tier" at all. It's just moving the technology forward
about 20 years or so (with 20-30 years of catch-up still to go). The
boards are single-layer and can be fabricated at home with that cool
laser-printer transfer stuff, the individual components are common and
inexpensive (except maybe the power transistors), and the construction
is both simple and flexible. The only major expense (other than the
power transistors) is the labor. Just hire a few illegals and you have
yourself a business! Or build it yourself with all the gold-plated
frills and LCD sensor array if you want. Or build it one module at a
time. Or buy the basic model and modify the modules as needed. It's
all up to the builder. Yet despite all the possible variations, the
basic design remains constant. That's the great part about a modular
design.