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

    Bump... This project has not been forgotten. Just temporarily 'on the shelf' so to speak...waiting for summer quarter to end (last one!), temps to lower a bit in the shop and then I'll hit this again. I have some additional components built, so will begin assembly of the RF deck soon... :)
  2. WB9ZIQ

    WB9ZIQ Ham Member QRZ Page

    Hi Vern,
    Ken's comments were right on. You can buy a sb200 used today probably for less than it will cost you to put together all the parts needed to build from scratch. Years ago there were hamfests loaded with old tube amp components, but now the pickings are rather slim. Your best bet is to find an old homebrew amp deck at a hamfest. That way you will probably have 90% of the parts for your project.
    I picked up an (2) 813 amp deck a while back that was set up for AB1 service. It has all the components there. Tubes, tube sockets, pi-network, solenoid choke, tune cap, load cap, parasitic suppressors, filament transformer, a tunable input circuit, meter, case, etc, etc. I don't think I could accumulate all the parts for what I paid for the amp deck. $75. The 813 is an extremely rugged carbon plate tube which has only one drawback. It's frequency top end is 20 meters. Reduced output on 15 and pretty shabby on 10. It will do a KW on the lower bands. Look around at hamfests this summer and you might be able to snag a project amp. If all else fails and you're interested in doing the 813's, I wouldn't be adverse to shipping it over to you for what I paid, plus shipping. I'm backed up on my projects and probably won't work on it anytime soon. Currently rebuilding an amp with a pair of 4-400A's.

    Ray WB9ZIQ
  3. N7GTB

    N7GTB Ham Member QRZ Page

    Hi Ray,

    Thanks for the comments and advice. I've tried saving up for just such an investment, but something always comes along that demands $$...

    As for the amp I'm working on now (also a 2x4-400a/c), I have 99% of the parts I need to complete it; and will likely set it up as a mono-band amp for 80/75 or 40 meters. The band switch is plenty adequate for the job, but the placement on the chassis isn't working out. But really, the largest issue now is time. Summer quarter classes end the 16th of next month after which I'll be able to focus on other things... :)

    Can you send me a couple of photos of your 813 amp deck? If you're interested in selling it, I have an 813 tube and would like to build up a mono-bander down the road for something like 160 meter operation...

    73, Vern
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    Finishing someone else's HB amplifier leaves one with a HB amplifier... without the pleasure of building it ALL yourself. If the sole object is to save money, don't HB at all.
  5. WW7F

    WW7F Guest

    Unless a ham considering making one already has a well stocked junk box. Then it is only time and a bit of power to use the soldering iron and power tools.
    Plus always remember, you can never have too much duct tape:) 73 Michelle;)
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    Parts availability aside, there are a few who are truly artists with tools, whose work is not easily distinguised from store-bought. And, there are many who should be banned from having tools in their hands.
  7. K9FV

    K9FV Ham Member QRZ Page

    From a purely cosmetic viewpoint, I'd guess those "truly artists" would ban me from having tools, but I sure enjoy learning and building.

    73 de Ken H>
  8. N7GTB

    N7GTB Ham Member QRZ Page

    I hope to have progress photos posted in a few days, which should include the main RF deck with sockets, rfc, plate connections, variable plate cap and *maybe* the loading coil. Too much job, school and family related stuff going on at the moment...

    I could use a consensus on opinions concerning building this thing for a single band to start, then possibly add other bands down the road...(?) The layout is similar to the amp described at WB0NNI's dakotamade site. Largest difference is that mine has the tubes mounted on a flat aluminum panel, as opposed to the 5" channel he used.

    Best 73,
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    Hi Ken,

    I wasn't pointing at anyone in particular. :)
  10. K9FV

    K9FV Ham Member QRZ Page

    Awwww Bryan - I knew you weren't pointing at me. I guess I had too much time on my hands today...... retired now<:)

    Vern - a single band amp is by far easier than an all band HF amp. Not only is the band-switching involved, but it's somewhat easier to get the tuned input and tuned output for a single band than trying to get all the different bands dialed in. Then at a later time, if desired, add the multi-bands...... Or perhaps start with two of your favorite bands?

    73 de Ken H>
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