Assembly Guide for the 222 MHz Kilowatt Amplifier Board

Note: The TC-12 supplied in your kit may be white or tan in color. See this tip for cutting the tan coax type.

 

 

 

 

 

 

 

Next, assemble the input board, installing the 9 to1 transformer and the input inductor last.

After the smaller parts are installed, solder the input transformer into place at the 5 red-dot locations

 

The last component to install on this board is the input inductor. For the BLF188, this will be an 8-turn inductor installed where shown. For the ART1K6, remove one turn to make a 7-turn inductor.
 

 

Install the output board components

 

 

 

Install the capacitors first.

The RF ceramic capacitors must be grouped in clusters of 3, and the clusters must be located where shown in the photo. Note the position of the polarity markings on the electrolytic capacitors.

 

Install the coax transformers; note the transformers nearest the transistor are placed right together, but on opposite sides of the area where the trace abruptly narrows.
 

Install the output balun
 

Install the two coaxial capacitors (the smaller one is installed near the transistor). After soldering, bend the coax ends so the open ends are clear of other parts.


 

Form the VDD drain chokes using the two pieces of #14 magnet wire supplied. Wind them in opposite directions (easier to install) on a 1/4" dowel or other form. Bend the ends as pictured.


 

Finally, install them as pictured here.


 

Install the boards onto the spreader with six 4-40 by 3/16 screws and flat washers, then solder the transistor tabs to the boards. Use a bit of flux when doing this to ensure a smooth, even connection.

Once the boards are installed, attach the spreader to your heat sink using the other 6 mounting holes. These holes are pass-through, so your heat sink will need to be drilled and tapped to receive the screws.

The two in the center are for 8-32 by 3/4 inch (or your metric equivalent) and do not require flat washers. The four in the corners are for 4-40 by 3/4 inch (or your metric equivalent) and should also have a flat washer under the head of the screw.


Testing:

Once you are ready to test, here's the recommended method:

  1. Connect the output to a wattmeter and a kw dummy load

  2. Connect the input to your driver through a wattmeter

     

    • CAUTION - for the initial test, you should place a 3 to 5 ohm 100w power resistor in series with the VDD, or use a current-limited power supply (limited to 5a). If there is a short from a stray wire strand, or a weak capacitor lets go, it will create an arc powerful enough to vaporize board traces, transistor tabs, etc.

     

  3. Turn on the 50v main supply voltage, but not the bias; there should be no current drawn

  4. Turn on the 12v bias supply and note the idling current drawn from the 50v supply. Adjust IDQ for 2 amps. Note: the current drawn by the bias supply (usually12v) is not what you are measuring here...you must measure the idling current (IDQ) the LDMOS draws from the 50v supply.

  5. Shut off the power supply, and remove current limiting.

  6. Drive with 1 watt or less. You should see an increase in drain current and at least 200w with 1w drive.

  7. Increase drive until you have 1kw out. Input power should be less about 5w, and drain current about 30A at 50v