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3-500z based amplifiers

Discussion in 'Amateur Radio Amplifiers' started by KJ4AQU, Apr 16, 2012.

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  1. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    Are there any inexpensive 3-500z amps out there that are well built and reliable? Maybe a contradiction of terms. I was look at the AL-80a or 80B but the B is over 1300.00 which i do not have. SB-220 possibly but power demands are high. Suggestions?
     
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    You can sometimes find a really good SB-220 that works properly and has good tubes for about $650 or so.

    They're all over the place.

    The Drake L-4B and L-7 can often be found in the $700 to $850 range, and those can be good deals, too.

    A used AL-80B is usually less than $1K and it's a solid amplifier.

    All this assumes they haven't been abused. I'd go for a "local deal" so I could look at it and try it out before exchanging cash for hardware.

    The power demands for the SB-220 aren't very high. A 240V 10A circuit will do it, and since #14AWG wiring supports 15A just fine, almost any 240V outlet will power it. Using one on 120V is pushing it.
     
  3. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    I Have found out that the 120v wiring in my house is using 12 gauge wiring. And circuit breakers are all 20 Amp Do you think
    it can handle a SB-220?
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Probably, especially if you have nothing else plugged into that circuit.
     
  5. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    That Drake L-7 looks sweet. But pricey. I'll probably try to concentrate on an Al-80a or B. A single 3-500z type.
     
  6. K1ZJH

    K1ZJH Ham Member QRZ Page

    The SB-220 is nice because you have two 3-500Z tubes sharing the load, and the SB-220 is a one kW and
    doesn't push the tubes as hard as the Ameritron amp. If you back the drive to the amp down to
    50 or 60 watts, the power demand from the AC line will be a lot less.
    Remember they are getting long in the tooth and may need new filter caps and other work.

    Pete
     
  7. W9GB

    W9GB Ham Member QRZ Page

    AQU --

    IF you are on limited or fixed income (usage of words inexpensive, pricey),
    moving up to 1 kW > amplifiers may be challenging.

    IF your current antennas, tuners, station accessories, etc. were cheap purchases --
    they may not be rated for more than 200 to 300 watts RF. They would have to be replaced.

    IF you can not afford the replacement tube(s) for the HF amplifier that you want to purchase --
    you can not afford that specific amplifier.
    Amateurs already have amplifiers in closets, storage, etc. with dead tubes -- they can not afford to replace.

    NEVER buy a used amplifier without seeing it operate -- unless you are prepared to restore it $$
    Something to think about, before committing to purchases.
     
    Last edited: Apr 17, 2012
  8. KJ4AQU

    KJ4AQU Ham Member QRZ Page

    Very True I put a lot of money into an SB-200 that I did not see tested. So for now I'll stick with an SB-200 class for now.
    or AL-811 which I currently have.
     
  9. AG6K

    AG6K Ham Member QRZ Page

     SB-220s operating on the LV tap do not much need to be operated from a 240V circuit. Operating on the LV tap only reduces output by 1.5db - or 1/4 of 1 S-unit. I can switch my SB-220 from the LV tap to the HV tap and no one at the Rx-end can consistently tell which tap its on.
    Fixing the design flubs in the SB-220 is fairly easy and doing so can save you much $$ as well as save you from grief. No matter which amplifier you purchase, remember that there is no such thing as a perfect amplifier - so be prepared to make some circuit improvements.
     
  10. KM1H

    KM1H Ham Member QRZ Page

    And since the 220 is an already low IMD amp it is even better when run on SSB on the CW position. No need to reduce drive, just run a typical 100W rig and it will self limit to around 750-800W out when fully loaded.

    Carl
     
  11. AG6K

    AG6K Ham Member QRZ Page

     On the CW/Tune position there is less ZSAC. Does less ZSAC give less distortion?
     
  12. W1QJ

    W1QJ Ham Member QRZ Page

    It was always my understanding that the linear curve of the amp was the same when switched from cw to ssb since the ZSAC changed as the Plate voltage increased keeping the amp still within the linear portion of the curve. Thus, the IMD should still be very good and distortion not a problem.
     
  13. AG6K

    AG6K Ham Member QRZ Page

     A pair of 3-500Zs is reasonably linear when the ZSAC is >140mA. On the CW/TUNE position ZSAC is c. 120mA due to the decrease in PS V.
     
  14. N7WR

    N7WR Subscriber QRZ Page

    The AL 80 A or B is a good choice. Solid amp that can easily be run on your 110VAC circuit.
     
  15. KM1H

    KM1H Ham Member QRZ Page

    Its actually a bit better Lou.

    The AL-80A is a bit problematic but the Amp Supply LK-450 is built like a rock, just stay away from the no tune versions.

    Carl
     
  16. W9GB

    W9GB Ham Member QRZ Page

    Just appeared on eBay, the Henry 1KD-5 HF amplifier (California seller) Item # 230781080358
    This Henry amp used one 3-500Z tube, this may be what you are looking for.

    w9gb
     
  17. AG6K

    AG6K Ham Member QRZ Page

     With 120vac/240vac input a stock 1KD-5 has 5.95v on it's 5v filament. This level of fil-V reduces emissive life to about 2% of normal so a new 3-500Z may be needed.
     
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