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Messenger M4V Best Operating Voltage?

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Old 04-21-2009, 12:29 PM
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Default Messenger M4V Best Operating Voltage?


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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Old 04-21-2009, 03:07 PM
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Quote:
Originally Posted by kd4e View Post
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
13.8 volts, you might add another battery if you like and an alternator capable of supplying atleast 120 amps.

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Old 04-21-2009, 03:37 PM
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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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Old 04-26-2009, 06:54 PM
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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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Old 04-26-2009, 07:01 PM
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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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Old 04-27-2009, 08:47 AM
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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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Old 04-27-2009, 08:58 AM
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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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Old 04-27-2009, 02:24 PM
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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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