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

    Used pair of 3-500Z based HF amplifier are the best bargain out there and the tubes are available new for a reasonable cost. But, the 'budget' priced pair of 3-500Z HF amplifiers are not equal in performance. Some amps struggle to achieve 1200 watts PEP out and some hams may believe two 3-500Z tubes always produces the legal limit power out.

    The following are what I consider to have a weak power transformer listed in weight. (Note- a 23 lb Peter Dahl C core is equal to about a 32lb standard IE lamination transformer that most amps use). The list below are commonly available amplifiers for sale. The B&W PT-2500 is somewhat rare.

    These are common amplifiers that should not be operated above 1000 watts PEP out, CW about 700 watts and RTTY at 450 watts out. The light weight transformers are the reason of the limited output from a pair of 3-500Z tubes.

    Ten Tec Centurion- 23lbs
    Swan MKII- 21lbs
    Heathkit SB-220- 23lbs
    Note- the single 3-500Z Ameritron AL-80B has a 26lb transformer and produces 1000 watts PEP out.

    The amplifiers below using a pair of 3-500Z tubes will deliver 1500 watts PEP out. The Drake L4 & L7 just make 1500 watts PEP out and require over 100 watts drive to achieve it.

    Amp Supply LK-500- 23lb Peter Dahl C core (equal to 32lb standard transformer)
    B&W PT-2500- 40 lbs
    Drake L4 & L7- 29lbs
    Henry 2K Classic- 42lbs
    Henry 2K Ultra- 38lbs
    Henry 2K Desk- 29lbs

    Note- some Henry amps had 3-400z tubes from the factory, but most for sale have 3-500z installed.
    Last edited: Nov 24, 2019
  2. G3YRO

    G3YRO Ham Member QRZ Page

    You don't mention the Kenwood TL-922 in your list , which also has a pair of 3-550Zs. . . that will produce 1200W output on CW.

    I have no idea what the transformers weigh, but it has separate ones for the HT and Filaments.

    Roger G3YRO
  3. N8FVJ

    N8FVJ Ham Member QRZ Page

    I cannot find any specs on the Kenwood, so I did not list it. The amp weighs 64lb so it likely has enough transformer to support 1500 watts PEP out. With 100 watts it produces 1200-1300 watts PEP so 120 watts drive should achieve the legal limit power.
    Last edited: Nov 25, 2019
  4. MM0IMC

    MM0IMC Ham Member QRZ Page

    Of course, you could always buy an aftermarket HV toroidal transformer for the job. It would certainly weigh less...
    N2EY likes this.
  5. N8FVJ

    N8FVJ Ham Member QRZ Page

    Yes, Peter Dahl makes replacement transformers that will make 1500 watts PEP out, but they cost $390 for the Swan & Heathkit and $537 for the Ten Tec + shipping costs. Also, about 120 watts drive for 1500 watts out after the new transformer is installed. That makes the weak transfoemer amps more expensive overall vs the 1500 watts output amps listed. The Peter Dahl internal mount transformer weighs 23lbs.
    Last edited: Nov 25, 2019
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    Why are you so hung up on Transformer weights ? And the heavier must be better ?

    Shipping WT, NET WT and Dead WT can be much different.

    Did you get your information from the internet that the heavier the better ?

    AI3V likes this.
  7. N8FVJ

    N8FVJ Ham Member QRZ Page

    Folks, disregard this rubbish.
  8. MM0IMC

    MM0IMC Ham Member QRZ Page

    Looks like most of the hams around here!:p
    KA9JLM likes this.
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    There are other parts in a power supply that are as/more important as the transformer.

    I like heavy capacitors.

    Just saying...
  10. VA3DXV

    VA3DXV Ham Member QRZ Page

    My CMC BH-30 weighs in at a rather stout 360 pounds. It will run a pair of 3-500's quite happily at 1500w, and will do it 24/7/365 with 60 watts of drive. If you're a size queen, find yourself one of those lol
    W1PEP, N2EY and KA9JLM like this.

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