600 watt HF Linear Amplifier Project

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

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  1. N1OOQ

    N1OOQ Ham Member QRZ Page

    Hey Ripley,
    Tks for the heads-up on the "lens tinting paint". Just what I needed for a minor project... putting a cheapo Chinese freq counter PCB in a box. See... I learned something in this thread! They sure don't give the stuff away, though.
  2. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Thomas,

    I don't remember what I payed for the tinting paint that I bought but at this point I don't much care. It's only money. :rolleyes:

    I moved a step forward this evening. I now can initiate a tune command from my transceiver, the linear amp will go into standby mode, and the LDG automatic antenna tuner will complete a tuning cycle without going into protection mode or generating some other error. That is a good thing. However, the transceiver keeps sending out a carrier continuously unless I push the TUNE button again on my Icom IC-7300 to stop it. In fact it is even more interesting than that. I request a tune cycle to start from either the transceiver or the LDG antenna tuner, The KEY line that runs from the antenna tuner to my transceiver and linear amplifier goes low causing the transceiver to send out a carrier and inhibiting the SEND line within the linear amplifier so that the antenna relay stays de-energized during this operation. The tune cycle is now complete but my transceiver is still transmitting a carrier so the IC-7300 thinks that I want to transmit and it energizes the antenna relay. My output power goes from 30 watts to 500 watts. Not a good thing. :(

    If I push the standby button on my linear to manual short the base of the switching transistor to ground with the KEY cable connected to the amplifier the same behavior is exhibited. Pushing the standby button again to remove the short only causes the amplifier to go from standby output power to full power. The only way to stop the transceiver from transmitting is to touch the TUNE button on the radio again.

    Hmmmm. My simple solution to insert a switching transistor between the relay coil of my bias/antenna driver relay and the SEND line to my Icom transceiver almost works but not quite. I think I might have to add another layer of isolation between the KEY line coming from LDG antenna tuner to my amplifier.

    More head scratching to do.

  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello folks,

    Well, I think I got it figured out.

    It took some fiddling with the switching transistor circuit for the antenna relay but now when I press the TUNE button on either the LDG automatic antenna tuner or my Icom 7300, the linear goes into standby mode, the antenna tuner matches the transceiver to the antenna, and when it is done takes the amplifier out of standby and puts it one line. No more High Power/SWR errors from the LDG AT-1000ProII. The antenna tuning process now works like a dream.

    That little exercise was resolved on Sunday so for the frosting on the cake I decided to add an LED that would light when the amplifier was in standby mode. Such a simple thing which turned out to be a major "Pain in the Bee-Hinder" to get working properly. The LED is driven from the circuit that controls when the amplifier goes into standby mode but due to several factors I couldn't get the LED to light only when I pushed the STANDBY button on the amp or when I pushed the TUNE button on the IC-7300. The LED wanted to illuminate whenever I was transmitting as well. Several pencil and doodle pad meetings with my Elemer at the Radio Museum later and we came up with an idea that I finally got working this evening.


    Now all I have to do is take the components from the bread board and mount them on the bias/antenna relay control board.



    Once I get the LED circuit built and installed in my amplifier I will report back with a schematic that details out what was done to make everything work.

    The best news is I don't have to chase any more dark magic RF issues with this project anymore.

    WA9WVX, AF6LJ and N1OOQ like this.
  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello again,

    It has been very busy at the Radio Museum so it only gives me about an hour or so in the evening to work on the amplifier. The components from the bread board were moved to the bias/antenna relay/12 volt regulator board.

    This board is a whole lot denser then when it was part of the amplifier mock up on the piece of plywood way back in the beginning of the year.


    Tomorrow I mount the Standby LED in the front panel, reinstall the board, and hopefully, do the validation test.

    Fingers crossed.

    AF6LJ likes this.
  5. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello RICHS,

    The LPF Diplexer board that I purchased from eb104.ru doesn't get warm at all including the high pass toroids and the resistors but I am only pushing about 600 watts through it. It is rated for a kilowatt. Here is a link to Victor's web site with detailed information including a video of that board in operation.


    He also makes LPF boards rated at 1600 and 2.5 Kilowatts.



    Once again I can't say enough good things about his products.

  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi RICHS,

    According to what Victor states in his description of the Diplexer board it will handle 2K+ watts in SSB mode. For the price ~$250.00 plus shipping from Russia, it is kind of hard to be the value.

  7. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Great progress Ripley. :)
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Thank you Sue.

    It is kind of anticlimactic but I installed the modified relay/12 volt regulator board in the amplifier this afternoon and it worked perfectly. Now I have to button it up and shoot a YouTube video showing how everything works together when I am operating the station remotely.

    You are welcome RICHS, enjoy your build and please keep me informed as to your progress.

    I have been going by Ripley since I was a kid. There are a lot of Bobs out there. We have one of the Alien eggs at the Radio Museum. Actually it is a tube rectifier for a coal mine. I think. It is very large and looks like a crystalline version of the egg from the movie. I will try to remember to take a picture of it.

    AF6LJ likes this.
  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    I can't remember anything anymore but I will try to take my camera with me to the Radio Museum tomorrow.

    Well I put the amplifier back together this evening and was getting ready to set it up for the demonstration video when I realized that I still needed to change the nomenclature on the front from BIAS-MANUAL to AMPLIFIER-STANDBY. You can see the LED that I added to show when the amplifier is in standby mode.

    I also need to label the RCA connector in the back which goes to the LDG automatic antenna tuner via a cable that I made specific for that purpose.


    Speaking of cables, in the picture below you can see the 1/8" stereo plug end of the LDG interface cable which goes between my IC-7300 transceiver and the LDG antenna tuner.


    It is the gray cable wrapped around the big toroid. Out of a bag of cables I came up with an 1/8" male stereo to two 1/8" female stereo adapter cable. Lastly, the special cable that I made is an 1/8" male stereo plug at one and a male RCA plug at the other. In this case I am only using the tip and the sleeve to provide closure for the circuit in the amplifier to put the amp in standby mode.

  10. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Very Good, looks good Ripley. :)

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