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EUREKA! IT'S ALIVE! :)

Discussion in 'Amplifiers' started by BJ radionut, Jan 27, 2015.

  1. BJ radionut

    BJ radionut
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    MY 6M AMP 12-001.jpg MY 6M AMP 14.jpg Well I must say it's been the most challenging and learning project yet to date for me.
    I started this with a Heathkit SB-221 chassis.
    You can see from the pics where I started, and now countless hours since my Christmas vacation. The project is working!
    My homebrew KW+ 6 meter amplifier is born.
    60 watts drive equals 1000w PEP on SSB.
    She will key down legal limit with 100 watts drive!
    Pair of 3-500z EIMAC tubes @ 3150 vdc at 750 mA plate current. MY 6M AMP 8.jpg PICT0023-001.JPG PICT0001-003.JPG

    CK/Warren/Crusher/Shockwave...I still have and issue with output at full 100w drive. I am getting audio distortion. I am guessing my limited experience with VHF building, my coax routing or orientation is the cause.
    HEY it's clean at 1000 watts, why sweet blood over 4-500 more!!!!

    Nobody will know the difference! Yes swing watchers NOBODY!



    So if you see anything that jumps out at you, let me know. When I decide to give it a custom paint job I may make the changes.
    Come on F2 and Eskip ! CAN YOU HEAR ME NOW!....ADD 13 dbi at 45 ft.... :)
    All the Best
    Gary/W9FNB MY 6M AMP 6-001.jpg MY 6M AMP 7.jpg
     
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  2. vkrules

    vkrules
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    Well done Garry would be awesome to work you on 6.
     
  3. Captain Kilowatt

    Captain Kilowatt
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    Looks good Gary. I forget what you have in the air for 6m but whatever it is a kilowatt will get heard for sure. I WILL get the six element HB yagi up this summer hopefully before Es is done for the summer. I should have the Larcan amplifier operation then as well with a full kilowatt and six elements at about 70 feet. Chances are if the band is even remotely open between us we WILL be able to make contact. LOL.

    Not sure what may be causing your issues off hand. Check everything for heat as some components may behave a little differently at 50 MHz versus HF. 6m is kind of too high for lumped variable components but too low for strip line. Some door knob caps may not like 50 MHz even though they are operating within their current ratings.
     
  4. BJ radionut

    BJ radionut
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  5. BJ radionut

    BJ radionut
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    Thanks Mark and CK also! Looking forward to working you both!:)
    I really enjoy 6m, just wish the band was showing more signs of life.
    Mark a few OP's have logged Zl/Vk's of late from Mid US states, but is tough from here!
    I listen and try to work Meteor Scatter on weekends when not working,
    (sunrise +/- 1 hour here local time) like 1100- 1300z ++
    I watch the ON4KST cluster and chat window during the weekends...(great bunch of OP's)
    All the Best
    Gary
     
  6. wavrider

    wavrider
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    Looks great Gary.
     
  7. Crusher

    Crusher
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    Looks good. I like the T match for input.
     
  8. Shockwave

    Shockwave
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    3150 X .750 = 2362.5 watts input power, exceeding the maximum capacity of the power supply. Efficiency seems rather low and may be the result of excessive C1 value loading the plate circuit down. The stray capacitance within the two tubes would be enough to tune the circuit so be careful not to add much more. If the tank circuit peaks out with the tune cap more than 25% meshed, you probably need to add more inductance to the tank coil. You might try compressing the coil wraps together some and see if that increases efficiency.
     
  9. Shockwave

    Shockwave
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    Another question I have is what's the idling current of the amp with no RF applied? I noticed the original bias zener diode behind the input circuit does not appear to be wired and I can't trace the black wire from the relay to see if it has been replaced with something appropriate. If it's running "Zero Bias" that's where the efficiency is being lost.
     
  10. BJ radionut

    BJ radionut
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    Shockwave: Great info! It's appreciated!
    Idle current = about 130 mA (+/_ meter accuracy )
    Plate Voltage under load drops to about 28-2900vdc
    BIAS: Using Harbach (Jeff/ W8CQ retrofit boards)
    The new board produces 6.8V of bias for the 3-500Z tubes, rather than the 5.1V...(from Jeff's website info)
    Tune Cap at Peak output is meshed...right at 50%
    Load C1 is (maybe) 10% past full open (Min Capacitance)...Which will be somewhere at 10-12pf...when I built that cap it measured like 8.4- 65pf on my B & K tester before install
    Can't give you inductance of tank coil....I copied the turns and diameter from other info on web....2 3/4 turns...approx. 1 1/4 diameter...3/8th's copper/silver plated tubing...3 inches from point to point mounting....

    Got to head to work...More later
    Again THANKS to ALL...It's a learning process...and this is why I'm here
    All the Best
    Gary
     
  11. Shockwave

    Shockwave
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    The tune cap (8.4 to 65 pf) should be adjusting below 50% mesh. At half mesh it's someplace over 30 pf and in many cases that would be enough to tune at 28 MHz. I suspect if you start compressing the tank coil to add more inductance, the tune cap will begin to adjust with less capacitance and the plate current should drop for the same output level once retuned.

    Consider that the internal capacitance of the two tubes is large enough to bring the tank circuit into resonance at 6 meters. The only real purpose to add the plate tune cap is so that the amp can be adjustable and tuned across the entire band. Therefore the tank coil should be tweaked so that the tune cap is barely meshed at the top end of the band and approach no more than 25% mesh at 50 MHz.
     
    #11 Shockwave, Jan 28, 2015
    Last edited: Jan 28, 2015
    Crusher likes this.
  12. Captain Kilowatt

    Captain Kilowatt
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    I wasn't even thinking about the power supply being under rated for that output. That could be the reason for the distortion at higher output levels. Gary can you look at the output with a 'scope and see if the RF waveform is flattopping?
     
  13. BJ radionut

    BJ radionut
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    Shockwave: Damn I was not awake this morning....I forgot I switched positions when I mounted the C1/C2 caps...I just looked at the front of the amp and started typing
    C1 is the Tune Cap...The 8-64 pf
    C2 is the LOAD Cap...the 20-150 Johnson...
    You already figured out I screwed that up when I typed that this morning
    C1 is only about 10% meshed
    C2 is right at 50%....

    CK: You and Shockwave nailed that one...Man I am getting old!...
    I know that stock SB-221 xformer can't handle that kind of stress!!!
    Further testing has shown key down with 60w drive to yield around 1100 watts with a plate current just slightly less than 600mA...Voice peaks of 1000 watts PEP at roughly 500mA...sounds a little better, but still Shockwave is correct the efficiency is not where it should be.
    100 watts drive sends it well over the ratings of the power supplies capabilities.
    Dinner Call
    More Later
    Thanks Men
    All the Best
    Gary
     
  14. BJ radionut

    BJ radionut
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    Well she's taking off, I'm afraid. I've got something major wrong.
    Just hooked it back up after "squeezing" the tank coil a little and now C1 is wide open(min capacitance) and the plate current went way up(showing a full amp).
    Output is a 1000 watts at 50w drive on the high voltage and the Idle current jumped to 2oo mA
    Low voltage 2500vdc(2000 under load) Idle current drops to slightly over 100 mA.
    50w drive is over 800w showing plate current the same.
    Well back to the drawing board! :(
    Swr on the meter going to the antenna shows like 1.2/1...which is weird I would think if it's going into self oscillation that would go crazy.
    Tubes are getting way to red comparing to what I see on the L4B even at 14-1500 out on HF....
    Well Gents any more advice? I thought I was close! Hey wrong again...
    All the Best
    Gary
     
  15. Moleculo

    Moleculo
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    Man that is a cool build. I just put this on the front page of the site because of how cool it is ;)
     
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