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Messenger M4V Best Operating Voltage?

Discussion in 'Amplifiers' started by kd4e, Apr 21, 2009.

  1. kd4e

    kd4e Member

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    What is the best operating voltage for a Messenger M4V?

    Mine has eight MRF-455's in the output instead of the 1446's.



    I have seen references from 12V to 17V, 17V seems too high. I am not as concerned with absolute maximum output as I am to protect the amp and to use the highest safe voltage in order to keep the current down some.

    I need to decide to either use several large deep-cycle batteries with a float charger or get a large AC-DC power supply.

    Also, if/when I use this mobile what secondary battery and other modifications should I make to my 1996 Chevy 1500 van to handle this amp? Upgraded alternator?

    Thanks! doc
     
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  2. mackmobile43

    mackmobile43 Jock Supporter

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    13.8 volts, you might add another battery if you like and an alternator capable of supplying atleast 120 amps.
     
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  3. kd4e

    kd4e Member

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    So even base where a higher operating voltage would be convenient 13.8 is optimum?

    OK re. the extra battery (perhaps an Optima or Deka deep-cycle?

    OK re. the 120A alternator - is that commonly available or what I have heard referred to as an "ambulance alternator"?
     
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  4. purenrg

    purenrg Member

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    My instructions sheet that came with my m4v only states a voltage of at least 13.8 volts minim, it doesn't state a Maxim voltage. I have run mine with as much as 16-17 volts. By running at this level I only seen about a 50w increase, it's safer to run it at 14-15 volts on a regular bases.
     
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  5. kd4e

    kd4e Member

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    13.8 minimum, hmmmm, I wonder if that is due to current-handling capacity? (Lower voltage = higher current.)


    I am wondering as the Motorola Spec Sheet shows 12.5V as the test voltage.

    Right now I am planning a US Battery US 12V XC 155aH (75A for 77min) with a 25A float charge.

    Perhaps I should add a big Farad cap to keep the voltage from sagging on peaks?
     
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  6. bob85

    bob85 Supporting Member

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    i have an old m4v with 455's, they use a crude bias circuit which runs hard into class ab, not as crappy as the texas star biasing but its basic with no regulation,
    early versions do have thermal tracking, later ones dont even have the tracking to help keep idle current under control,
    mine pulled 9 amps of idle current and got hot with no rf through the amp,

    running a stock m4v at higher than stock supply volts is asking for cooked transistors.
     
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  7. kd4e

    kd4e Member

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    Sounds like 13.8V is about right then.

    Have you made any mods to improve the bias circuit that you could share, please?

    Any other improvements?

    I presume that some of the combiner-splitter and transformers may need to be replaced in order to improve efficiency - yes?

    I am hoping for 40-10M, dreaming of 80-10, 160-10, or even 160-6M ... WDYT?
     
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  8. bob85

    bob85 Supporting Member

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    i removed one of the parallel dropping resistors in the bias circuit to lower idle current to 1 amp, bit of a bodge but it still sounds decent on ssb and runs much cooler,
    no other modifications, it deadkeys around 620w fm with 10w drive on the bird or lp-100 meter using whatever voltage the stock 90amp alt can provide, thats more than enough for 8 mrf455's imho.
     
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  9. kd4e

    kd4e Member

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    [FONT=Arial,Helvetica]I just read this description about the [/FONT][FONT=Arial,Helvetica] Metron MA-1000 amp:[/FONT]
    [FONT=Arial,Helvetica]"A high speed 75 Amp Magnetic Circuit Breaker protects against short circuits, overdrive, and mismatched antennas. A protective diode will not allow the amp to operate if the supply polarity is accidentally reversed. A 75 degree thermostat mounted on the heatsink will switch off the amp if the temperature becomes excessive."


    I have not yet received my M4V - are any of these features in the M4V?

    If not do you see a way that they may be added?
    [/FONT]
     
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  10. bob85

    bob85 Supporting Member

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    the m4v has 3 reverse polarity diodes, no thermal switch and no vswr/overdrive protection,

    a thermal switch bolts to the heatsink and wires in series with the on/off switch, simple enough if you dont mind making a hole in the board,

    overdrive and vswr protection would be a squeeze but it could be added, theres not much room to fit a vswr bridge between the relay board and the output filter, you would also need a suitable circuit and know what you were doing with it.
     
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  11. kd4e

    kd4e Member

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    [FONT=Arial,Helvetica]I am guessing that the "high speed 75 Amp Magnetic Circuit Breaker" is sensing current surges and is tripping - an alternative to a superior but more complex VSWR sensing circuit.

    WDYT?

    I will also need to do something about band-switch filters.
    [/FONT]
     
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