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

    Hello OZ,

    Yes sir, my little amplifier has been working well. There are seven radios in my ham shack these days and the IC-7300 paired with that little home brewed amp gets it's turn in the rotation about every other week.

    Knowing what I know now, if I were to build this amplifier again today these are the changes that would be made:

    1.) Either install everything in a larger cabinet and add more shielding or install the power supply in a separate cabinet and add more shielding in the amplifier cabinet itself. RF bouncing around inside of that smallish cabinet that I used has messed with the digital displays for power output and SWR and just recently lead me down a rabbit hole trying to figure out why I was showing a drop in the DC supply voltage while keyed down in CW mode. The amp was working fine I was just getting erroneous readings from those digital displays.

    2.) Use analog meters to show output power and SWR. I think analog meters would look better with that 70s stereo look that I was going for when I designed the cabinet. Also, as mentioned above, I think they are less prone to RF interference from inside the cabinet.

    As for the support boards that I purchased indirectly from EB104.ru I see that the particular protection boards that I used are no longer available. However looking at the eBay reseller's site where I ordered my boards I see that there are similar offerings.


    The low pass filter board that they sell now is similar to what I purchased except mine only went up to 10 meters. There's covers up to 50 Mhz. https://www.ebay.com/itm/Low-pass-f...747044?hash=item3b0d368424:g:UdAAAOSwfLJa-uZh

    The protection board they sell now looks like they have combined the power supply protection and high SWR protection boards into one module. https://www.ebay.com/itm/Protection...008393?hash=item3b3f2d5e89:g:5kEAAOSwKM1b88~n

    The RX-TX switching unit and Tamdem match module are now on one board. https://www.ebay.com/itm/RX-TX-unit...372422?hash=item3b12510e46:g:sGMAAOSwrzxbMLge

    The only things that I don't see is the attenuator board and the Power Output and SWR LCD display module but the later can be obtained from other eBay suppliers like this one. https://www.ebay.com/itm/SWR-Power-...5&algv=default&_trksid=p2047675.c100008.m2219

    I wish you the best on your build and please take this bit of advise for what it is worth to you. The project is going to take much longer to build then you think it will and cost a whole lot more than you thought it would. :)


    KK4CUL likes this.
  2. OZ6TI

    OZ6TI Ham Member QRZ Page

    Hi Ripley

    Thank you very much for your quick and comprehensive reply. I really appreciate it.

    I just bought the stuff from the links you suggested - SWR & PWR Meter were sold out, but I finally found it on the italian ebay. Buying the other stuff just worked out fine. Yes, it is expensive to buy stuff and to do things yourself. You should no be a homebrewer to save money... Apart from all the bits and pieces, also shipping cost have gone up dramatically due to the corona, as the operators are having severe difficulties getting the goods on regular flights as there are still not many of these...

    Yes, I already decided to have the power supply outside the cabinet. The same goes for the LP filter. I like the flexibility of not building to much together. I was intriged by this low-pass filter https://www.wimo.com/en/lpf-1. I find it good priced and with very fine specs. And it is fine with me that it goes to 10 meter only.

    Yes, it is probably going to take a while before I am on air with the PA - and it may not be the last time, I am contacting you :)

    All the best!


  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Ole,

    That is an interesting looking low pass filter. I would be curious to see what it looks like on a spectrum analyzer. What are you going to use for the PA board itself?

    Enjoy your build and hunt me if you need me.

  4. DK7OB

    DK7OB Ham Member QRZ Page

    This low pass filter is looking like a standard "TVI" filter with a cut off frequency above 30 MHz. I'm not an expert, but don't you need band specific low pass filters for an amp?
  5. G0GSR

    G0GSR Ham Member QRZ Page

    Yes, you absolutely need a bank of switched LP filters. A single LPF with a cut-off at 40MHz is not adequate.
  6. N7EKU

    N7EKU Ham Member QRZ Page

    Yep it's an old-fashioned TVI filter made for the days of tube-transmitters (which weren't always clean enough).

    You can get them on ebay for $10.

    Probably still a really good idea for unfiltered, over-driven, CB amps.


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