First Homebrew HF power amp

Discussion in 'Amateur Radio Amplifiers' started by N7GTB, Jan 9, 2012.

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  1. N7GTB

    N7GTB Ham Member QRZ Page

    Thanks Ken. My goal is to use it for HV supply. It's dimensions are nearly identical to WA7PRC's dual bobbin unit, so I'm thinking it should be similar in terms of power capability... Getting the laminated core apart without tearing it up, is proving to be a bit time consuming! -V.
     
  2. KA3ZLR

    KA3ZLR Ham Member QRZ Page

    Hi my name is Jack,

    I have an spare 4-1000 if you wana just build a one lunger... an go big..

    73
    Jack
    KA3ZLR
     
  3. N7GTB

    N7GTB Ham Member QRZ Page

    Hi Jack, Thanks for the offer, but I'm still learning here... Someday (maybe) I'll press my 5CX1500A's into service...which should be plenty big. :)
     
  4. N7GTB

    N7GTB Ham Member QRZ Page

    I just finished reading through another thread here: http://forums.qrz.com/showthread.php?292934-New-linear-project&highlight=TRANSFORMER+rewind in an attempt to learn more about transformer rewinding... Needless to say I learned more than I expected, but I'm wondering if it answered enough of my questions to proceed with the rewind (sorry, just thinking 'out loud' now).

    My gut tells me 'No'...(says he, whilst still peeling laminates out of the core). So without going back to school for my EE degree, is there a good source of design information besides (please read this as 'in addition to') the site by Ludens? The spreadsheet at his site clearly seems useful, but I'm having a hard time understanding what constitutes a reasonable value for flux density. In the spreadsheet, this seems to have a major affect on the KVA rating and efficiency... I realize this may seem pretty elementary to some here, but I'm still trying to wrap what's left of my alleged brain around all this...:confused: I've been assured that the transformer is large enough for my needs and I'm willing to trust that... I'm just trying to gain a better understanding (if that's possible), of the steps required to assess that (ok, does that make sense? hope so!). :) Do I need to know more about the core material and it's properties, or am I simply over-thinking this whole thing...?

    Thanks & 73,
    -Vern
     
  5. N7GTB

    N7GTB Ham Member QRZ Page

    Ok, so after some forehead slapping I now I realize that I've been working this problem in reverse of what the approach should be... i.e., - start with the required plate voltage for a particular tube then work towards the xfrmr primary. In my case given the size of the core, it makes sense to use a voltage doubler...so divide the desired plate voltage in half... I've done all this before with low voltage supplies, but it's been years. The spreadsheet by Ludens makes a little more sense when coupled with a separate sheet that does some simple calculations to derive the secondary voltage. :p

    73,
    -Vern
    p.s., still working on that power transformer. Will try to post another progress pic tomorrow...
     
  6. N7GTB

    N7GTB Ham Member QRZ Page

    More of a good start, but at least it's a start... Only about an inch of the core has been removed. I work full time (and go to night classes 4 days a week), so this is a "when I can" project... :)

    IMG_0140_small.jpg IMG_0142_small.jpg IMG_0143_small.jpg

    ...the above shows a little over an inch of material removed.

    73, N7GTB
    -Vern
     
  7. N7GTB

    N7GTB Ham Member QRZ Page

    Had some extra time this weekend, so went to work on this beast...

    IMG_0146_small.jpg IMG_0148_small.jpg

    ...finally! Now to build a mandrel and turning jig! The windings from that transformer weigh in at approx 15 lbs.
     
  8. K9FV

    K9FV Ham Member QRZ Page

    Hello Vern, You're making GOOD progress and keep us posted on progress with those good pics you do. I've been away from QRZ for several days due to no access, but should be around more now. I remember the thread you linked to above, and it does have a lot of good info. Bryan, Tom, and especially Owen - and several others have contributed to my small store of knowledge on amps. A buddy and I both are interested in building a HV transformer, so I WILL be following your project. I'm looking at full time retirement by end of March so will have more time to pursue these "important" projects {grinning}

    A project like this is worthy of it's own thread.

    73 de Ken H>
     
  9. N7GTB

    N7GTB Ham Member QRZ Page

    Ok gang, I could use some feedback here. Below are my numbers for rewinding...

    (if I can find, build, steal a dual bobbin winding form then I'll use it, otherwise it looks like it will be a layered winding...)

    To recap, the core has a stack height of 4" (~ 101.6 mm) by 2.5" (63.5 mm) wide. The window is 1.25" by 3.75"...
    Assuming Tesla = 1.2 I have the following:
    KVA = 2.495
    Primary (@ 240VAC): 116.4 t, 10 amps with #14 AWG
    Secondary: 888.3 t @ 1.36 A with #18 AWG

    This should (and here's where I need verification of my numbers) give me adequate power to drive a single GG GS35B at ~ 1400W out (max)... I'm thinking of adding taps for lower voltages to accommodate other tubes.

    I would appreciate help but please be nice... Thanks! :)

    73,
    -Vern N7GTB
     
  10. N7GTB

    N7GTB Ham Member QRZ Page

    One thing additional I should mention here, is that I only plan to use this on SSB. I don't do much CW and am not set up for RTTY, etc.. -V.
     
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