This means I'll need to Digi-Key $30 more for the case and shipping but it will give me 1" more thickness to work with and the entire heat sink to mount stuff. It will also be massively larger than it needs to be for even 100% duty cycle use.. but bigger is better here like in many things.. :O)
But because of this I decided to start mounting the stuff from the center of the heat sink out..
Here is a small green Sharpie with markings of the AN 729-140 Amp, the K5OOR HF Projects amplifier board and a VSWR bridge that I've built. this leaves all of the aluminum on the right for the microcontroller. The little bit on the left will have to house the 20 mW to 5W Class-A amp and maybe the TR relay.. but I could mount the TR relay on a bracket also.
Even at 12"x7" it will be a little bit tight if I stay with one layer of boards. I'd like to also put an Aluminum shield in between the amp and the microcontroller, too... that'll be on the right too.
Look good enough. Lets drill and tap. The only way to get this all accurate enough is to use a drill press, the #43 drill and actually drill through the holes on the board and transistors. The "dots" from the Sharpie are not precise enough. Take your time, and do one corner first.. drill and tap and screw down. Do the opposite ("kitty") corner.. drill, tap and screw.. then do the remainder of the holes. This goes for both the AN-729 board and the K5OOR board (which is really tight tolerance!). For the RF transistors.. I partially drilled the holes with the MRF-454 in place and then finished them off with the transistor removed. Be very careful when doing this.. but it's the only way to get precise enough holes with home equipment. This is probably the most delicate and most important part of the build and is probably the most important part to get right for the amp to work.
There are five holes-- the standoff holes and the D1 hole to drill for the PC board. Then there are the four screws to secure the MRF-454's to the board. All need to be precisely drilled and mounted. Take your time and use plenty of tap oil when tapping Aluminum.
The K5OOR 100W LPF board has 4 mounting holes also that should be drilled/tapped. These are extremely tight tolerance (the 4-40 screws basically take a little of the solder off in the plated through hole they are that tight) so get these right too.
Here is what is should look like when done. I'll save anyone building this about $20 at the hardware store to show you what is needed for the perfect fit needed for both the D1 bias (thremal runaway preventer) transistor (used as a diode, B-E junction is used).. and the proper 1/8" spacing for the MRF-454's. I could only get nylon for spacers.. and they didn't fit well. I bought a whole box of 4-40 Stainless Steel flat washers.. and low and behold.. 4 of the under the board spaces the board perfectly for both D1 and the MRF-454's. (D1 mounts in the middle of the board.. it's just sitting at the edge to show the board spacing fit!) Of course, the 4 washers under each screw are impossible to mount underneath unless you bind them together somehow. A drop of Krazy Glue brand super glue (cyanoacrylate ester) carefully applied when four of them are on a 4-40 screw works well enough to hold them together for placement under the board. This means that a total of twenty-one stainless steel flat washers-- including the top washers- are needed for the AN-729 board alone (buy a box of 100 from Ace Hardware if you are getting them locally--it will be less than 25 at piece rate). There are 25 of them in this picture on both boards. The D1 2N5190 transistor is maybe 1/64" shy of 1/8" but I figure that you could either mount it flat and let the board bend inwards a little (what I'll do) or put a washer under and over and have the board bow out a little. D1 needs to have silicon heat sink compound on it and have the metal tab side down towards the heat sink.. but securely wedge with the center screw... drill and tap that hole as well.
The Pass transistor Q3 on the bias regulator circuit (pass transistor for the LM723G or MC1723G regulator IC) does NOT attach to the heat sink. DO NOT drill a hole for it. The original 2N5989, 2N5990 or 2N5991 transistors that were suggested for this design are all obsolete (and are available, but from $7-13 each!). There is no newer transistor that has the odd-ball pinout that these transistor had, so a 2N6488 TO-220 cased transistor is substituted. The transistor needs to be mounted upside down and hardware is supplied for that but nothing else. I wish the 1/8" spacer supplied for that could have also been supplied for the four standoff corners, but CCI clearly doesn't sell these as kits, but boards and parts.
The screws needed are quantity 4 - 1/4" long Stainless cap screws (cap screws are needed here) for the MRF-454. The board screws are quantity 5 - 3/8" long Stainless cap screws ... washers on top.
On the K5OOR 100W LPF.. the mounting is 1/4" aluminum spacers (Ace Hardware) with 1/2" long 4-40 SS Cap Screws and a 4-40 washer on each. I had to go to two different hardware stores to get enough SS cap screws to do this job.. so some are from Ace, some are from True-Value. True-Value is cheaper.. Ace had more selection. :O)
Here are a couple more views of the test fit. It's vitally important to get this all correct before mounting parts on to the boards. You should spend an afternoon doing this alone.... maybe two...
I also fixed that old power supply.. and added +3.3V/0.8A LM1117-33T to it this weekend see below:
I also built a TR relay based on the one in the Communications Concepts EB-63A amplifier. I probably will only use this particular circuit for the initial use. Eventually I'll have PTT in and Microcontroller based RF "VOX".. but for initial build and testing a good RF-sensed relay will be handy.. it was only about 1 hour of work. Two more Teflon RF cables need to be soldered on.. but some future evening for that... 2N3904's were substituted for the 2N4401's and 1N914's were used instead of 1N4148's. I didn't have a 1.5K resistor handy in non-SMT, so I used two 3.3K in parallel. It's all not that critical. I actually think the SSB delay could use a bigger delay.. maybe a 33 uF cap instead of the 22 uF electrolytic? We will have to see in actual use. There are 0.1" headers and jumpers for the SSB delay and from the diodes (so that the RF sensing could be bypassed and a +5V keying could be used instead...) Break is at D3 and C11..
So that's it for this weekend. It didn't seem like I did a lot until I sat down here tonight and documented it all...
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