[Lowfer] 500kc web site updated

[W5JGV (Ralph Hartwell)]

Hello everyone!

I just updated the http://500kc.com web page to add some links to the
Version 2.02 of my 200 watt amplifier.  I also added a few links to the
PDF files of the solid state components and a high-res JPG of the
breadboard setup, which I'll try to describe in this message.

V2.02 adds a few things, such as the ability to switch between linear
operation and square wave switching mode operation for CW.  In either
case, a low-level sine wave signal may be used to drive the amplifier.
None of the parts values have been set in stone, and a lot may change
between the breadboard and the finished unit.

There is a mini ferrite bead placed over the gate leg of the MOSFET's,
otherwise it's oscillation city!  You can see the beads on the
transistor leads in the picture on the web site.

I also replaced the LM386 with an LM384 (NTE862), which is a 5-watt
audio amplifier.  It works much better at 500 KHz than does the LM386,
and produces a lot more drive.  The picture shows a pair of copper heat
sinks attached to the LM384 as per the data sheet, but since the actual
output power is very low, they proved to be unnecessary, at least in the
breadboard version.

DESCRIPTION OF THE PICTURE:

In the upper left of the picture is the low voltage breadboard power
supply.  The amplifier PA stage is in the lower left.  There are two
separate electrically insulated heat sinks, one for each MOSFET.

The PA output transformer is above the top of the heat sink, and is
supported by the primary leads.  Note that the primary is wound on top
of the secondary for better coupling. The brown secondary leads are seen
pointing to the top of the breadboard, and these leads connect to a
twisted pair of wires that connect to the gray 50 ohm load resistor seen
just above and to the right of the two blue electrolytic capacitors.

Right behind the output transformer is a small computer case fan with a
cardboard air duct to direct the air through the heat sinks.  Note that
these heat sinks and fan are good for 200 watts output, but only for
about 30 seconds, and then you have to start with the heat sinks cold.
USE A BIGGER HEAT SINK!  These are just for breadboard tests.

There are two bypass capacitors, one gray and one black, that are
super-glued to the heat sinks.  These bypass the B+ and the bias lines
for RF.

At the bottom center of the picture is a horizontally mounted pot with a
gray knob.  This pot sets the MOSFET idle bias.  on the right hand heat
sink, you can see a black plastic clamp, set at an angle, with a pair of
yellow leads emerging from beneath the clamp.  This is the 10K NTC
thermistor that is used to stabilize the bias when the heat sinks get
hot.

At the bottom of the breadboard is a silver pot, which sets the symmetry
of the analog to digital conversion function in the TC4426 MOSFET driver
IC.

Towards the top left of the breadboard you can see the LM384 amplifier
IC with the pair of home made copper heat sink plates attached. Below
the amplifier IC is the switch that changes between linear and digital
mode.  The amplifier tuning requires a different resonating capacitor
for the linear and the digital modes; I'm still working on an easy way
to change the caps when changing modes.  Also the B+ should be changed
when changing modes.  Digital mode requires less B+ than does linear
operation.

To the right of the switch is transformer T1.  Below T1, and somewhat
hidden by the forest of components is the 8-pin TC4426 MOSFET driver IC.
Since the input of this IC is running in forced analog mode, it tends to
be very sensitive to electrical noise.  Good grounds and short leads
(which this layout certainly does not have!) are essential.

More updates to follow, as I get the time to work on this little goodie.

73,

Ralph   W5JGV - WC2XSR/13

My Amateur Radio and Rife Project files are at:
http://w5jgv.com

The ARRL 500KC Experimental Group is at:
http://500kc.com

My Tesla coil pictures are at:
http://www.spectrotek.com