Buy Smart- 3-500Z Amplifiers with weak HV transformers

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Nov 24, 2019.

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  1. N8FVJ

    N8FVJ Ham Member QRZ Page

    Actually capacitors are not more important. Capacitors do not supply power to the power tubes, they filter the DC only. A healthy sized capacitor bank does reduced the voltage drop during transmit peak output.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Transformer weight isn't everything.

    An example is: Acom (Bulgaria) uses a 4CX1000A in the ACOM 1500 HF+6m 1500W PEP output (1200W rated continuous-duty 24/7 carrier) powered by an strip-wound Unisil-H core HV transformer weighing <30 lbs. It's a brute. The whole amp is only 58 lbs.
    The 4CX1000A is currently manufactured and $495 (or less) brand new, like here: This is just slightly higher cost than a pair of new 3-500ZGs and these have an extremely long storage life so a spare purchased today is very likely to be fine 30 years from now.

    Of course, Acom also manufactured the 91b for Alpha, which used a pair of 4CX800As and was also pretty bruty.:p
    WA7PRC and KA9JLM like this.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    My 8877 amp seems heavy duty. It has a 24/7 continuous rating, At the cost of a high electric bill.

  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    Cannot buy anything that comes close to your 8877 amp.
  5. N8FVJ

    N8FVJ Ham Member QRZ Page

    A lot of tube for the money.
  6. KV6O

    KV6O Ham Member QRZ Page

    I have a QRO Technologies HF-2500DX, running a pair of 4cx800a's. It weighs 90lbs, the plate transformer is 40 lbs.+ of that, IIRC.

    Do I win something? :p
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    I rewound a transformer that came to me in a free scrapped medical power supply. The new secondary uses 18 AWG wire. A fullwave doubler rectifier yields 3338, 3581, 3827 or 4073 VDC at well over 1A all day:
    The two tapped primaries were meant to make it usable worldwide (100/120/200/240V, 50-60 Hz). The split bobbin gives it very good pri-sec isolation, and allowed me to not have to touch the primaries.

    My material costs amounted to about $140 for 10# of heavy-build polyimide-coated wire, and Nomex-Mylar-Nomex "paper". I had enough leftover for another rewind. A local transformer shop vacuum-pressure impregnated it w/ polyester resin free gratis, to reduce magnetostriction noise. :)
    N2EY likes this.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Sure you can! It just takes money.

    The same guy who designed most of the very BIG Henry amplifiers like the 8K Ultra etc. has his own business now, ASI, which is only a couple of miles from me. His "smallish" HF amps use 3CX3000A7s and most are rated in the 10kW output area, but he'll make and sell them to hams if they're willing to pay for them. The bigger tube amps are mostly water cooled. Charlie's still at it!
  9. W1BR

    W1BR Premium Subscriber QRZ Page

    These are not fair comparisons... just because an amp may have two 3-500Z tubes does not imply it was designed to be a legal limit amplifier by today's FCC standards. Many of those amps were made when legal limit was determined by plate current times plate voltage for a 1 kW max input. Besides, there are other considerations besides the transformer rating: air flow and cooling, PA tank component ratings, etc.

  10. N8FVJ

    N8FVJ Ham Member QRZ Page

    Pete the comparison is fair. A pair of 3-500Z will provide legal limit output (1500 watts PEP). The limiting factor of how much the tubes produce in power output is the transformer. I did not say the weaker power transformer in the amplifiers design is inadequate with regard to what the amp was designed for, just what the amp will produce in power output without stressing the power transformer. The SB-220 was produced when the FCC rules were 1KW input. Way more than enough transformer for 1KW input. However, many hams think a pair of 3-500Z tubes produce 1500 watts out and if they want that power the amplifier itself must be considered.
    Last edited: Nov 27, 2019

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