600 watt HF Linear Amplifier Project

Discussion in 'Homebrew and Kit Projects' started by KD8UYQ, Feb 9, 2017.

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  1. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    http://www.mrtwv.org/Hello Sue,

    There is a large chunk of aluminum under those two finned heat sinks that I made on my milling machine in which the TIP122 is mounted and that keeps the temp on that transistor down to about 113 degrees F. When I move that board to the metal cabinet that I aquired for this project the power supply protection board and the +12 volt regulator will be mounted to one of the steel metal sides with an additional heat sink or two.

    Regarding the heat from the PA board, it amazed me as to how well that copper heat spreader works. I used an inexpensive Infrared Thermometer pistol from Harbor Freight to take temperature readings. It works well when pointed at a black or dark color surfaces but the accuracy falls off when aimed at lighter color or reflective surfaces. The 175 degree reading was taken with the IR Thermometer pointed at the black finned heat sink. I neglected to take a reading on the transistors themselves but they were much cooler to the touch compared to the heat spreader or heat sink. The MRF150s are rated for a Total Device Dissipation of 25 degrees C (77 degrees F) and I was way over that. None the less they suffered through my abuse and still work fine. However, I'm not going to push my luck.

    Hi Ed,

    I don't think you will be disappointed if you purchase Victor's LPF diplexier board. I'm not. What kind of medical amplifier did you harvest the BLF-278s? The reason that I ask is because I use to be a biomed tech in the mid 70s then went to HP as field service tech for their healthcare division, then eventual to healthcare equipment sales until my retirement fourteen months ago.

    Now I am a volunteer Docent and all around maintenance guy at the Museum for Radio and Technology in Huntington, WV.


    The curator has also been an adviser on this build and one day he disappeared into the museum's basement and came back with this cabinet.



    It was a project box that was donated to the Museum years ago along with a whole bunch of other item. The steel metal box measures 11" wide by 8" tall by 12" deep. It cost me a $50 donation to the Museum and I think that was a deal. You can see that I already started cutting holes to mount the power supply and PA board.

    Below are pictures of the cooling fan mounting arrangement that I engineered.



    Note that the 120 mm cooling fan for the heat sink is spaced back about an inch. Since those pictures were taken the mounting bracket have been painted black to match the cabinet.

    Fingers crossed, I hope to be back on this build soon. It looks like I fixed the AGC problem with the Yaesu FT-980 on my workbench and will be running it for the next 12 hours or so to see if my repair did the trick.

    Tomorrow I am back at the Radio Museum all day. We have a massive project to go through and update the thousands of Sam's Photo Facts that we have received as donations over the years.

    Anyone want a box or two or ten of duplicate Photo Facts?

    KV4PD likes this.
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    That is a nice case. :)
  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Sue,

    I like the cabinet too. I wanted something that could accommodate both the power supply and the amplifier in on box.

    Well you folks are almost caught up with where I am to date on this project. Just a few more details to highlight; a second and third relay are going to be incorporated into this build. The second relay turns the linear amplifier on and off when the transceiver is powered up or turned off. This is for remote operation. Currently I can power up and shut down the Icom 7300 from my laptop and I want to do the same with my amplifier. Relay number two is connected in parallel with the power switch. The third relay is to by pass the linear completely should I choose to run a transceiver "barefoot" with the linear amplifier off. RF is routed through the third relay and out the SO-239 connector of the linear amp bypassing the PA board completely. The second relay has already been installed and tested on the mock up board but I will hold off on the third relay until I move everything into the cabinet.

    I mentioned before that RF is getting into some of the displays but hasn't interfered with any of the control lines for the protection board or LPF diplexer board. The digital voltage display works fine no mater which frequency is selected but the current display shows 0.0 amps when I push power above 6 watts. Also the LCD power display gets a bit wonky depending on the band but I'm not too concerned about any of this. All the circuit boards and sub-assemblies are laid out on a piece of plywood with no shielding of any kind. When I relocate all of this stuff into the metal enclosure and add shielding then I will address and stray RF issue that may arise.

    Lastly, the cabinet itself. My other passion is building remote control scale model aircraft. It is not uncommon for me to spend upward to three years building a model and getting all of the details right. For example this is my T-34B that I built for contest flying. The wingspan is 80", it weighs 20lbs, and everything works. The landing gear retracts, the canopy sections slide open and close, landing and navigation lights can be turn on or off from my transmitter.

    T-34 pic 1 3-23-13.JPG
    T-34 cockpit top left view 03-10-13.JPG

    Finished Cockpit 5.JPG

    So with that in mind I want the cabinet to look nice. I'm thinking something with a partial smoked gray or bronze Plexiglas front panel with the power output/SWR display and selected band LEDs illuminated from behind. Something clean and elegant in appearance with walnut side panels, kind of like what a 70s Pioneer stereo receiver use to look like. With the power turned off two thirds of the front the panel would look like a shiny black monolith. Then when you power it up the shiny black box would comes to life with a soft green and blue glow.

    That, my friends, is where I am headed next.

    KK4CUL, WA9WVX, K9FV and 4 others like this.
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    Wow that's impressive.
  5. WA4SIX

    WA4SIX Ham Member QRZ Page

    It is 1/2 of an AMT amp. I am not impressed by the heat sink, but figure it was for a pulsed application. I have a spare Larcan 1.5K pallet that I will pull the BLF 278s from to put in the AMT. I will probably chop down the Larcan & use the last 2 MOSFETS for a 600W 2M amp, as I just hate to see amplification devices laying around.

    At work, I am getting 16-600W 48V switcher supplied that did not like the noise from our Beckhoff servo controls, but can be ganged together with the IC2 line.

    I work in automation. Latest gig was flying Lady GaGa in the 1/2 time show... If you happen to see people flying at the Academy Awards show, I might have something to do with that, too.
    I get lotsa spare or failed junk from work... Luckily, I have 2-10X12 sheds to store it.

    I will order the Diplexer this weekend, so that when I finally have a lull in work, I can get everything mounted in a 90s vintage Larcan UHF TV amp rack mount enclosure.

    Of course, that may be several months, due to R&D for new equipment at work. I am the guy that gets 20 sheets of paper with drawings & schematics from the tech director & gets told to make it work.... LOVE my job !!!

    Last edited: Feb 24, 2017
    AF6LJ likes this.
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Ed,

    Sounds like you have an interesting job. As for me, retirement suits me just fine.

    I think I finally figured out what was wrong with the Yaesu transceiver on my work bench, parts on on order and I should be back on this amplifier project by next weekend.

    AF6LJ likes this.
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    Being self employed most of my life, due to ADD/ADHD & the sheer boredom that comes after a year or so, I just love where I am now. If I come up with a crazy idea (Often), I get to try it. I may not have the knowledge to design it, but after some time with the tech director, we make a general plan & I go to work.
    I get paid to PLAY with lathes, overhead mills, stamp presses, MIG/TIG, shears, breaks & the such. They like me, because, I have not only the electrical/electronic knowledge, but also the mechanical aptitude to follow through to completion.
    We used to have a pile of electronic scrap outside that the Meth Heads used to pilfer. Now, I take stuff home & sometimes repair to the point that we can use something in the shop for experimentation purposes.

    Yeah... I love my job.

    KM1H and AF6LJ like this.
  8. SWL37632

    SWL37632 QRZ Member


    Outstanding thread. Keep us posted!

    AF6LJ likes this.
  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Winston,

    Will do.

    AF6LJ likes this.
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    I am back working on the EB104 Linear Amplifier project. The holes in the back of the cabinet have been punched and the connectors fitted.

    cabinet rear view.JPG

    The SO-239 connectors on the left are RF in (top) and RF out (bottom). Over on the right is the power connector with integrated fuse tray and above it the control cable connector from the Icom IC-7300. Over on the front you can see that the holes for the power switch, the power LED, and the three digital displays have been made with those components test fitted.

    Years ago I use to have my private pilots license and flew Cessna aircraft of different types. The instrument panel in a Cessna, like in most every other airplane has primary and secondary instrumentation. The primary instruments are place squarely in front of you while the secondary instruments are situated below or peripheral to your field of vision. I carried that idea forward to the layout of this amplifier's front panel. I don't need to contentiously monitor the voltage and current going to the PA board or the temperature for that matter but I do want to do a quick scan of all three from time to time. For that reason they are mounted towards the bottom of the cabinet. Kind of like my flight training I do a left to right scan of the most important instrument first. In this case It is temperature, followed by currently, than voltage. I prefer the blacked our style of the blue temperature display but unfortunately I haven't found a blue LED current and voltage display that have the brightness that I like and/or match the criteria that I needed in a blacked out style.

    The upper part of the cabinet will be smoked dark gray or bronze Plexiglas trimmed at the top and bottom with a thin bright aluminum bezel. Just off center of the Plexiglas section will be the 2" band select knob. All of the band indicator LEDs, the fault condition LEDs, and the Power Output/ SWR display will illuminate from behind the Plexiglas window.

    The first step was to figure out the exact placement for everything.


    To be continued.

    KK4CUL and AF6LJ like this.

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