GM4ULS ham radio station

a QRM-free zone!

Zetagi B300P

Posted by gm4uls on November 21, 2011

The AT5555N is driving the Zetagi amp quite nicely. 5W AM from the former produces 100W from the latter quite comfortably, but I generally run about 40W.

When you buy a Zetagi you get what you pay for. There are no frills to this unit. It looks like it was made to compliment a 1980s CB, so teaming it with the AT5555N is just right. I’m using it quite happily, so the following niggles are just that – niggles.

  1. The ‘manual’ is a slip of paper giving bare details, a circuit diagram so small you need binox to read it, a picture of what plugs in where, and that’s it. Nowhere do they give you a clue about what the six-way switch is; it is, I’m informed by someone who knows, a six-stage attenuator which cuts the amount of power you are inputting on its way to the power transistors, and I had to ask around a lot before I got that answer! Memo to Zetagi: find room on the slip of paper to explain that, it ain’t rocket science.
  2. The pre-amp doesn’t work. Not only does it not work it seems to attenuate to the point of muting the receiver. Not that this matters a great deal as the AT5555N is sensitive enough on receive. I’m told that this is not an unknown fault.
  3. The claimed output power of 300W (PEP on SSB) is a touch ambitious.
  4. It runs hot. Very hot. I could just about boil a pan of water on the heat sink. I have got round this by mounting a small fan behind it. Pic below.
  5. Zetagi don’t waste money on a power lead; you get about six inches. Pic below.

This is the fan - it was robbed from the insides of a defunct computer.

This is the... ahem... power lead.

Overall verdict, well, the whole set-up works and I get good reports. Clickety-click, job done. Today I had a QSO with an American station who had never heard of either the rig or the amp. So that was fun too.

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6 Responses to “Zetagi B300P”

  1. Hans said

    I guess that Zetagi is really cheap? You got a real nice setup there for 10, I should say. The Anytone is known here as K-PO, and the latest version (V5) addresses many of the problems described in the review you linked to in a previous posting. Apparently the manufacturer is reading all this, too.

    Maybe we can have a sked on that NYC repeater one day.

    • gm4uls said

      Hi Hans. I’m on KQ2H most days at about 12:00z, or any time after then. Of course I can’t guarantee the propagation – today’s Tuesday and it’s already 11:45 and there is no sign of a signal…. ah here it comes, still a bit weak…

      Yes the K-Po DX5000 is the same rig as the AT5555 and about half a dozen other ‘clones’. By the way I just measured the output on SSB – with 5W in and with attenuation on 2, I was peaking at 150W. I shall be trying a few more careful tests in the next few days.

  2. Gene said

    Hi chap my names Gene call sign g6zdb. Some time ago was given a blown up b300p,with both pa devices gone so all i had to hand was a pair of mrf422,s so i did the board repair to resistors and such added a voltage stablizer to the bias circuit and put higher voltage caps in . as now it works any where between 10volts and 30 volts . so topping over 350 watts out with 20 watts drive. The very nice thing about all this is i can run it on constant carrie , using fm or am and dont have to worry about cooking them .so the out put devices came out xmilitary kit and are so good i get good gain from 80meter through to six meters . so….oooo…. i need to build my self a bigger power supply as the max 30amps on my manson want handdle the amp on full . next is to mod the preamp for a lower noise device . not forgetting conecting the relay 12 volt regulator . its wounderful watching the watt meter take off lol . good job o have a 3kw watt harmonic multi band swith fillter in the output line . As dont want harmonics every where lol. A D V A N C E D S E M I C O N D U C T O R, I N C.
    REV. A
    7525 ETHEL AVENUE

    NORTH HOLLYWOOD, CA 91605

    (818) 982-1200

    FAX (818) 765-3004 1/1
    Specifications are subject to change without notice.
    CHARACTERISTICS
    TC= 25
    OC NONE
    SYMBOL
    TEST CONDITIONS MINIMUM TYPICAL MAXIMUM UNITS
    BV
    CEO
    IC = 200 mA 35V
    BV
    CES
    IC = 100 mA 85V
    BV
    CBO
    IC = 100 mA 85V
    BV
    EBO
    IE = 10 mA 3.0V
    I
    CES
    V
    CE = 28 V 20mA
    h
    FE
    V
    CE= 5.0 V
    IC = 5.0 A 10 30 120

    C
    ob
    V
    CB = 28 V
    f = 1.0 MHz 420pF
    P out
    V
    CE = 28 V
    f = 30 MHz 150W (PEP)
    G
    PE
    η
    η
    η
    η
    IMD
    V
    CC = 28 V I
    CQ = 150 mA
    P out = 150 W (PEP)
    IC(max) = 6.7 A
    f = 30 MHz
    10 13
    45
    -33dB
    %
    dB
    NPN SILICON RF POWER TRANSISTOR
    MRF422
    DESCRIPTION:
    The ASI MRF422 is Designed for 2.0 MHz to 30 MHz, 28 V High PowerLinear Amplifier Applications.
    MAXIMUM RATINGS
    I 20 A
    V 40 V
    P DISS 290 W @ TC = 25
    O
    C
    T
    J
    -65
    O
    C to +150
    O
    C
    T
    STG
    -65
    O
    C to +150
    O
    C
    θ
    θ
    θ
    θ
    JC
    0.6
    O
    C/W

  3. Gene said

    so hey ho 290 watts times 2= need big power supply lol m

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