600 watt HF Linear Amplifier Project

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

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  1. WA4SIX

    WA4SIX Ham Member QRZ Page

    Thread forming taps do not have cutter edges. We use them for aluminum over 1/8" at work.

    AF6LJ likes this.
  2. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hmmmm. Interesting information on the different kind of taps. I never heard of a thread forming tap but I have now.

    Hi Reg, When I decided that I wanted to build a solid state amplifier my research lead me to the EB104 and the Russian made protection boards. Making everything from scratch was more than I wanted to tackle so this project is more of a cobbling together of all ready available sub-assemblies. Even at that I had a whole lot of help. I'm just passing the help that I received along to others.

    After the bias voltage and current was dialed in on my PA board, I had no excuses. It was time to see if my amplifier would work. At the time I had no idea how much heat this EB104 board would generate so I wired two 40 mm fans in series per the schematic for the power supply protection board and pointed them at the heat sink.

    PA mock up with fans.JPG

    I have a little Kenwood TS-120 transceiver that is perfect for testing projects like this. It is so simple to operate that making an error setting up the radio is pretty slim.

    Pretest check list.

    A. Output of the linear connected to my Telewave Watt meter and a 1000 watt oil filled dummy load
    B. Set the Telewave for 500 watts and FORWARD to display the output power.
    C. Connect the output of my TS-120 to the input of the linear amp
    D. Transceiver set to CW on 40 meters (7.250 Mhz)
    E. Transceiver carrier control set counterclockwise to minimum
    F. Power up the linear and check to see if I have 600 mAs showing on the LED display
    G. Manually select the 40 meter LPF and check to see if the LED light for that band is illuminated
    H. Power up the transceiver


    So far so good. The nice thing about the TS-120 is that I don't have to key the transceiver to output a signal. All I have to do is flip the Send/Receive switch to Send and slowly bring up the carrier by turning the carrier knob clockwise.

    Here we go. Transceiver Send/Receive switch flipped up to SEND and slowly increase the carrier. It didn't take much drive. With the carrier control set to the 7:00 position to start, at a tad over 8:00 I was seeing 500 watts out on the Telemwave.



    Here is what the signal looked like on my scope.


    And Spectrum Analyzer.


    To say the least, I was over the moon. My amplifier works!

    I only ran the output up to 500 watts because that is full scale deflection on the Telewave but I have no doubt that it will easily put out 600 watts and possibly a tad more. I will test that when everything is moved into the cabinet.

    A couple of thing that I should point out. When I first powered up my amplifier the Russian digital display was telling me that I was putting out something like 1100 watts. Turns out that it wasn't calibrated so I adjusted the Forward Power trimmer pot on the back of the display to better match what the Telewave was showing me. RF is getting into display so it's accuracy at different bands is questionable but I will address the RF issue when the boards are inside of a metal cabinet. Surprisingly the SWR reading was pretty close to what the Telewave was telling me when I measured the reflected power. I will adjust that too when everything is in it's permanent home.

    Power output on all bands is 500 watts but it takes a bit more drive at 15 and 10 meters. Speaking of drive, At 40 meters, 30 watts into the input protection board gets attenuated down to about 7 watts out to the PA board for a final output power of 500 watts. At 10 meters it needs about 40 watts in to get 500 watts out but I haven't made any adjustments yet to the trimmer capacitor that bridges the input of the Transmission Line Transformer on the the PA board. The worse internal SWR that I have measured on any band is at 10 meters where it calculates out to be 1.35. At 40 meters the SWR is 1.22.

    Well that is my update for this evening


    KG5RKP, NL7W and AF6LJ like this.
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    So, with the spectrum analyzer, it looks that the Russian Diplexer filter is to specs? I am looking into it for a project. Would you let us know when all bands are tested for harmonics. I will be using 4-BLF278s in a medical amp.

    Thank you,
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    Good Deal, glad to see all is working.
  5. N7EKU

    N7EKU Ham Member QRZ Page


    Nice job for sure! Since you have an SA, can you show a bigger span so we can see the upper harmonics?

    Cheers and 73,

    AF6LJ likes this.
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    Ed, I only took a peek with the spectrum analyzer at 40 meters to see if the diplexer was working but I can check the other bands after everything is in a metal enclosure. When I measured the second order harmonic and it was down -54 db and you can just see the third order harmonic to the far right of the display and that one is down around -50 db as referenced from the peak.

    Bottom line: They are both way down there.

    Thank you Sue.

    Mark, let me see what I can do. At the moment I have had to set this project aside. I am working on a local ham's Yaesu FT-980 with an elusive AGC problem. This radio has all the makings of a "Tough Dog" problem.

    K9FV, WA4SIX and AF6LJ like this.
  7. N1OOQ

    N1OOQ Ham Member QRZ Page

    Awesome. How hot did it get?
    AF6LJ likes this.
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Great question.

    When I first fired up the amplifier I did a lot of testing with the amplifier running between 150 to 500 watts. The cooling fans run all the time but kick up to full speed when the heat spreader warms up to 131. It didn't take long for that threshold to be crossed. The two little fans were trying their very best to cool down the heat sink but it was like bailing water out of a boat with a cup. When I finally finished my testing the heat sink was at 175 degrees. Thermal shut down is at 176. The amplifier got pretty hot but suffered no ill effects however I order two 120 mm computer case cooling fans from Newegg.

    Now that I have a working amplifier it was time to make the control cable between my IC-7300 and the linear, wire up the control cable within the amp, and test the remote control functions.

    You can see in the picture below that a gray cable has been added between the Icom remote control board (small board right of the band selector knob) and a connector between the RF input and PA boards. There is another gray cable attached to that connector and exiting left of the picture to my IC-7300. Also note how big the heat sink below the power supply board is getting. There is a power transistor under those twin pair of fins that supplies the voltage and current to the fans and the two voltage regulator ICs.


    One of the hardest things to make for this project was the interface cable. It was no simple task to solder many tiny wires onto tiny pins so that nothing shorted when the connector shell was in place. It took three tries and some insulating tape before I got it right. Testing went well. Touching the display on the 7300 to change bands caused the linear to respond in kind. I must admit that I played with that function for a good half hour because it was so cool. The white wire dangling off of my work bench is the Push To Talk line to the transceiver. That wire was later connected to a 12 volt relay that was added to the +12 volt regulator board. The purpose of which is to apply the bias voltage to the PA board when I am transmitting and then disconnecting it when the transceiver is in receive mode. 13.8 volts is available out of the IC-700 accessories connector and is wired to one side of the relay coil. The other side of the relay coil is connected to the PTT line. When you push the PTT button on the microphone or activate the transmit key on the transceiver the circuit is completed and the relay pulls in. I tested that function and it worked well. With the bias voltage only present on the PA board during transmit it helps to lower the overall operating temperature of the amplifier.


    Good evening.

    KK4CUL likes this.
  9. AF6LJ

    AF6LJ Ham Member QRZ Page

    That was the first time I got a good look at that heat sink.
    I would have gone with a much larger heat sink. That really does look too small.

    One other thing...
    I would keep those transistors down to somewhere around 50C and mo more, I am sure you are exceeding the safe operating area.
  10. WA4SIX

    WA4SIX Ham Member QRZ Page

    Remember to not have the new fans bolted directly to the heat sink, as there is a no air section at the hub. 2" or so away should be fine.
    I like the Diplexer filter, due to the harmonics getting dummy loaded, instead of reflected back, or circulating.
    I spent way too many hours designing one for my amp, then found the RU one that you have. Glad to hear the preliminary specs & that is enough for me to hit the "Buy" button.
    I will have 4-BLF-278 (MRF151G)s from a medical amp. I already have 6 of them from an old Larcan TV LO band transmitter amp for 6 meters. It sure can open up the band quickly...
    If you were closer, I have a few large rack mount cases you could stuff it all in. I think they are 5U size & full depth.

    AF6LJ likes this.

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