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Polamar 350Z Amplifier

Discussion in 'Amateur Radio Amplifiers' started by KC2SPU, Aug 3, 2018.

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  1. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Where did you get that idea? I've designed (from scratch) almost every amplifier I've ever used on the air, and still have four of them. I've published the construction articles, and you can find them on line, complete with schematics, parts lists, and many photographs.

    Give up.:p

    February 1985 issue of CQ magazine shows me and a friend (KT2B) inspecting my workmanship on my new 4-1000A homebrew (and fully home-designed) 1500W 6m amplifier.

    That was a full construction article with lots of photos, schematics, parts lists, etc. in a different issue. I still have that amp, it still runs 1.5kW output power, the anode runs bright red key-down at 1500W out (same tube since 1984), and I tune it up entirely by watching output power and grid current. It's the only way to assure it's properly loaded.
    Last edited: Aug 9, 2018
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    A slicker article because it really was designed from scratch to be "easy to build" is the 8877 amp article I published in June 1987 CQ.

    That wasn't taken from any existing design: Just used the 8877 data sheet and engineering knowledge to design and build it, and it still works very well. It also meters grid current and output power for tuning.:) Of course, the power supply current limits at about 1.2A anode current so even running this off-resonance for hours won't hurt anything as long as grid current remains low.:p

    Anyone interested should look up the article: Since I sold it to CQ they have the copyright and I can't republish the entire article anywhere; but it's loaded with diagrams, parts lists, and lots of photos during and after construction. It's been duplicated by a lot of hams -- I get the letters, sometimes with questions, to this day.

    June 1987 CQ contents.PNG
    VE1FAR likes this.
  3. VE1FAR

    VE1FAR Ham Member QRZ Page

    Just look at that tube. Awesome work Steve.

  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Looks better in operation at 1.5kW output, key down CW, for a long time.

    The plate glows so bright red you could read a newspaper by it.:)

    It was intended to operate that way, for 10,000 hours. In BC service, that's only a bit more than a year (!) but in amateur service...golly, mine is 34 years old now and probably doesn't have 10K hours on it yet.
  5. AI3V

    AI3V Ham Member QRZ Page

    Then you should be happy to share your construction notes Steve,

    Or by designed do to mean assembled from donated parts, for a magazine article designed to sell radio parts ?

    Runs 1.2 Amps at how many volts,

    Let's see mr ohm, watts that ?

    But you don't have to worry about anode resonance, cause you got a grid current meter

    There is a reason that magazine went out of business decades ago.

  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What in the world?

    The magazine is doing fine, alive and well and still sponsoring a few of the biggest contests in the world.

    The 8877 amp operates at 3.2kVdc B+, current limited to 1.2A.

    Normal operation when tuned is 3.2kV @ 0.8A for 1.5kW RF output at 50 MHz.

    To tune it you tune PLATE for a grid current peak, adjust LOAD for output power peak, re-tune PLATE for grid current peak, and re-adjust LOAD to set Ig to 20mA maximum. Takes five seconds. Optimum loading with 20mA max Ig puts the amp on the most linear part of its I/O curve and it's not even 1 dB compression.

    The amp does meter Ip also but other than glancing at that once in a blue moon, there's no reason to look at it.
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Here's a bit about the 4-1000A amplifier, article published in 1985. I can reproduce this because I own the copyright on this one.

    It was actually a "one weekend" project, start to finish, with hand tools, a benchtop drill press, a set of Greenlee chassis punches, etc. Built the power supply first (it's very heavy), then the RF deck. The power supply hides on the floor, the RF deck sits at the station bench.

    Still puts out 1500W with a 34 year-old tube.:p
    4-1000A amp article.PNG 4-1000A amp article 2.PNG 4-1000A amp article 3.PNG

    All parts were purchased by me, including a brand new Dahl hypersil transformer for the B+ section (but some other parts were surplus from Fair Radio and such), new meters from Amp Supply, and a "pulled" tube from a local FM Broadcast station: About $400 total for everything (in 1984).

    I use the same power supply for two other RF decks: A 4-1000A for 160 meters and a multiband amp with a pair of 4-250s.
    VE1FAR and WA7PRC like this.
  8. VE1FAR

    VE1FAR Ham Member QRZ Page

    Hi Steve
    could this 4-1000 amp be adapted for 40 or 20 meters? I think it would be nice to have a low drive amp. I do have a QRP transceiver (elad duo) that could use a boost.
    Would the same input circuit work?
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I built a nearly identical 4-1000A amp for 1.8 MHz (only -- not bandswitched) and it works very well. It produces 2.3kW output power with ~25W drive (into a dummy load) and for 1.5kW only requires <20W and runs smoothly.

    No, the same input circuit wouldn't work; the one shown is optimized for 6m and has pretty low Q on purpose, but only covers about 48-52 MHz or so.

    Obviously for 20m or 40m, the tank components need to be much larger! I shoot for a Q of around 10 or so, but a bit lower doesn't hurt. There are pi-net calculators on line you can use: You enter plate load impedance, antenna load impedance (assume 50 Ohms), resonant frequency, and Q and it will provide the C1, L1 and C2 values. I used a vacuum variable in my 6m 4-1000A not so much because they're great, but because the one selected has very low parasitic inductance and very low minimum capacitance. On HF, that doesn't matter much and an air variable with sufficient spacing will work fine.

    You'd need a different input network of course and a calculator will determine those values, also. And you'll need a different plate RF Choke for sure (lots more turns) but a similar form and mechanicals can be used.

    If you're serious about homebrewing one and want me to look up all the values, let me know and I can do that.

    The power supply is a larger project than the "RF" part, especially for a grid-driven amp where you need very low dynamic impedance grid and screen bias supplies.
    N8VIL and WA7PRC like this.
  10. W2WDX

    W2WDX Subscriber QRZ Page

    I mean seriously Rege, what? Are you daft or do just live to make a fool out of yourself. Look guys its just time to ignore this guy. I seriously think he just posts to push buttons.

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