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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

    Hi Bill,

    The ground strap that I tried yesterday was indeed a length of 1" wide .030" thick solid copper ribbon. It made no improvement so I did not install the ground strap.

    Wiring is not an issue. When I retired back in 2015 I worked with the electricians to covert my daughter's bedroom into a hamshack and a electronics work station. These guys were great. They installed a sub panel in the hamshack closet and gave me four 20 amp circuits with outlets galore.

    Ripley
     
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  2. N1OOQ

    N1OOQ Ham Member QRZ Page

    Of course 20 ft. is a substantial fraction of a wavelength on most of HF...
     
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  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    In my dogged pursuit to get this linear amplifier done other electronic projects have accumulated around the workshop to the point where they started to get in the way. I took this week to take a break and put the amplifier aside so that I could tackle those projects including this nifty vintage capacitor checker.

    DSC_0480.JPG
    and this Heathkit SB-630 that I bought at Hamvention this year.

    DSC_0482.JPG
    I had to make a new lens for the clock window among other things to bring the control station back to working condition. Just have to paint the cabinet and it is good to go.

    Meanwhile, on Monday I sent an email to the support folks at LDG describing what was going on with transceiver, linear, and automatic antenna tuner setup and here is what they said.

    "Hello,

    Included here is the tuner interface document that shows how the interface works.

    We would highly recommend that you never have the amp on when tuning the AT-1000ProII. Since there are many type of amplifiers and interfaces, you may need to build an interface or sequencer that makes sure the amp is placed in standby when the tuner is tuning.

    I hopes this helps understand the tuner.

    Sincerely,"

    Attached is the application note that they sent me. Testing so far has shown that the Icom IC-7300 works with the LDG auto antenna tuner on all band flawlessly every time. It's only when the amplifier is turned and in circuit that the antenna tuner fails to tune and match to the antenna.

    Looking at the application note and talking to my Elmer at the Radio Museum today we came up with a plan but it requires that I do a modification to the linear amplifier;s circuit that operates the PA module bias and antenna relay.

    Those other projects are done so hopefully I can state working on the modification to my amplifier this weekend.

    Fingers crossed.

    To be continued.... but I dearly hope, for not much longer.

    Ripley
     

    Attached Files:

  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello RICHS,

    Your bad feelings were well founded. I was under the mistaken impression that when I initiated a tune command from my transceiver or from the LDG tuner itself the tuner would throttle back the drive to my linear, tune and match to the antenna, then increase the drive power back to where it was before the tune botton was pushed. I now know that the interface cable only provides contact closer. What the linear amplifier or transceiver does when it sees a input signal line going to ground is completely up to the manufacturer. Apperently, if you have an Icom radio, an ALS-600, and the LDG AT-1000ProII the behavior that I described above does occur but that is because the Ametron amp knows to attenuate the drive going to it when the tune signal line goes low.

    I need to modify my antenna relay circuit so that when I push the tune button on the Icom transceiver the linear goes into standby mode until the tune cycle is done then the PTT line will become active again. That is certainly not how my amplifier is configured now.

    The light bulb went on when I received the email from LDG and read the application note.

    Ripley
     
  5. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Thinking about it a little bit more, I bet that all that happens with the Icom, ALS-600, and LDG antenna tuner setup is the ALS -600 is also put in standby mode during the antenna tuning operation. Nothing more than that.

    In a nutshell, the LDG automatic antenna tuner is designed to tune the exciter by bypassing the linear amplifier then when antenna is matched to the radio the linear is taken out of standby mode and brought back on line.

    Looking back, when I first started this project I knew nothing about building a linear amplifier, then I gained a thimble full of knowledge, and now I am up to half a teacup. :)

    Ripley
     
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello RICHS,

    Fear not, I am actively working on my amplifier and will be posting an update soon. Most of the support boards in my amplifier came from EB104.ru. I highly recommend his products.

    http://www.eb104.ru/

    Ripley
     
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  7. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Looking forward to the update. :)
     
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    I am so close to getting my amplifier 100% operation but "no cigar" as yet.

    I changed the bias control switch (always applied to the PA board verses only applied to the PA board when the transmit button is pushed) into an amplifier standby switch. Now I have no problems with the LDG automatic antenna tuner doing it's thing when I manually place my amplifier in the standby mode. My only problem now is to have my transceiver control that operation when I press the Tune button on the Icom IC-7300. I designed a remotely controlled Standby circuit based on the assumption that when a tune request is not activated the input to my new little interface board is an open circuit. Turns out that Icom has +3.2 volts DC sitting on the Tune line to the LDG antenna tuner and, in turn, to the base of the switching transistor that actives the standby circuit in my amp turning it partially on. The net effect is my amplifier is always in standby mode. I have to play with my remote control standby circuit a bit but I feel like I am almost there.

    It is late or me here on the East Coast and time to put my head down but I wanted to give you a quick up date.

    Ripley
     
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  9. N1OOQ

    N1OOQ Ham Member QRZ Page

    I am amazed at your perseverance, Ripley.
     
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  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Thomas,

    I have come so far and am at the point that the solution to this one last issue is almost within reach that I can't give up now. Besides, to put things into perspective, if I was build another R/C scale model for competition purposes I would only be half way through year one of a three year project. Talk about perseverance consider working on the same project every week night for one and half to two hours plus another 5 or so hours every weekend for three years until your creation is completed. That takes dogged determination to see your creation through to the end.

    Not much to report this evening. I am working everyday now at the Radio Museum for at least the next two weeks so I can only spend about an hour our two in the evening working on the amplifier. Tonight I basically undid what I created the night before.

    Ripley
     
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