CONVERTING THE AVANTEK 10 WATT AWP-64100 LINER FOR 5760

BY NR6CA

The conversion of this amplifier to Amateur service at 5760 first involves removing the two heatsinks. There are lots of small screws that need to be removed in order to get the heatsinks off. Notice in the photo below that there are at least 15 of them. You also need to remove the nut and washer on the attenuator adjustment potentiometer which is just below the power cord in the photo below. This is the adjustment that can be used to set the overall system game to accept anywhere from -1 dBm (<1 mW) to about 10 dBm (10 mW).

The photo below is what the amplifier looks like once the top heat sink has been removed. The DC/DC convertor is at the bottom and the RF deck it on the top. Looking a the RF deck, the SMA input is on the left side and the 10 watt SMA output can be seen over the label on the right and blocking the letter "E" in Avantek. Just below the label on the far right side is the attenuator adjustment potentiometer.

This next photo is the DC power distribution board attached to the side of the RF deck. The adjustment potentiometer is on the right and is standing vertical. In Jeff Kruth's conversion he suggested removing the right end of the board, just past the visible mounting screw at the edge of the chassis and using a different single resistor to replace the bank of resistors on the board and then remoting the potentiometer and wiring it back to the remaining section of board. I decided not to do this since not a lot of space or weight would be saved.

This last disassembly photo is of the entire RF deck removed from the heatsink with the power distribution board still intact. The heatsink and the bottom of the amplifier will both have some thermal compound on them, I suggest wiping this off to make things less messy while cutting the heatsink down. It rubs off with a paper towel of rag pretty easily. The input is on the left and the output is on the right side. In the photos both above and below, the bottom heatsink has also been removed separating the RF deck from the DC/DC converter. In order to cut the heatsink down to a smaller size, these pieces all need to be separated. Then each of the heatsinks can be cut as required.

This next picture is the top heatsink after having been cut down to its new size with the RF deck bolted back on. Since you removed it in an earlier step, make sure you use a little thermal compound here to enhance heat transfer. Don't get carried away with it, you only need a thin layer. Too much is not a good thing. I didn't get the heatsink cut to be as straight as I wanted but it is OK. My suggestion for cutting the heatsink down to size is to first mark it just wide enough to fit the amplifier and the DC board. This one is cut wide enough to also keep the attenuator adjustment within it but I have decided to relocate the adjustment over near the SMA output connector.

This photo shows the amplifier bolted back onto the cut down heatsink looking from the DC distribution board. I filed down the cut edges so as to not get cut by them. I Then drilled three holes with a #29 drill and tapped them for 8:32 threads. I will cut a sheet metal plate to fit over the DC board to protect it using these three holes. The picture below this on shows a close up of a tapped hole. Be careful tapping the holes since aluminum tends to bind up. I suggest running the tap in the hole 3 turns or so and then taking it back out. Then go in another 3 turns or so, and remove it. You can even turn the heatsink on end and tap it on the work bench to entice some of the smaller pieces to come out. The aluminum is soft and tends to bind the tap which might cause it to break off.

Now let's talk a bit about cutting the heatsinks. This is not the easiest thing to do but there are some simple ways to get the job done. Of course if you have access to a band saw set up for heavy metal cutting the job can be done fairly easily. A few other techniques that can be employed include a Sawzall, a saber saw, portaband saw, a table saw or even a circular saw. However, I DO NOT suggest using a saber saw (jig saw) since the blades tend to fill up with the soft aluminum which then causes them to bind up. The saw starts to vibrate like crazy, is hard to hold and quite often the blade will break.

By putting a carbide tipped blade on a circular or table saw (use a SHARP one) aluminum can be cut pretty quickly. However, this is a very noisy method and tends to throw small pieces everywhere. No matter what method you use make sure to use both eye and ear protection and wear heavy gloves. Be certain to tightly clamp the heatsink to something so the cutting device can't throw it at you or through that nearby window!

What ever method you use to cut the heatsink, just be careful. You can also make a cutting guide by clamping a piece of wood along the line to be cut.

I will at some point add some actual test data and some thoughts on providing power from two 12 VDC batteries as well as other power supply options.