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MOSFET Question

Discussion in 'General CB Services Discussion' started by CTStallion, Jan 6, 2014.

  1. sonoma

    sonoma
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    I have just over 50 radios out with the 13n10 mosfet and never had one blow as of yet. a buddy up in New Jersey has about 100 out and he has not had 1 blow either. what is the gate voltage of the Stryker radios when the mosfets blow? if some one gets ahold of the 13n10L mosfets they only will take 2 volts and blow.


     

  2. wee electronics

    wee electronics
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    There are two versions of that part, one that is set up for logic level drive 2V at the gate and the non L version. There is also the possibility they may have gotten a hold of some counterfeit parts. I don't have near as many out there as you guys do, probably about 30, Ive had at least 6 blow ups on NEW radios. We are seeing more power out of the Vishay IRF520 using a dummy load and LP-100A Digital Vector meter. My point is, its not worth messing with to gain a watt or two.
     
    Captain Kilowatt likes this.
  3. Captain Kilowatt

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    [QUOTE="wee electronics, post: 572961, member: 48812" My point is, its not worth messing with to gain a watt or two.[/QUOTE]


    People really need to learn more about dB's and what they mean and less about what a power meter says. My favorite is the single final to dual final conversion for some radios. Lots of work to gain an extra 3 dB at MOST ie half an S-unit.
     
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  4. wee electronics

    wee electronics
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    I agree, I created a chart in excel and then made a graph of it to illustrate your point to my customers. Some of them don't comprehend the meaning of logarithmic. 400 to 500W is the best bang for your buck. Anymore and you are just throwing away money
     
  5. sonoma

    sonoma
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    I like the 13n10 better because the way I do them I do not use the companion part that is out or even build one. the 520 and 13n10 both go in the way I install them and the 13n10 runs cooler using a digital thermometer to check the temp. stated out using the irf520's and a guy talked me into trying the 13n10 mosfets and I just liked them better. I even use them in the Rm kl203 amps when the factory ones are blown. I run the gate voltage at about 3.2 to 3.5 volts. do not try to get a lot out of them like Captain Killowatt mentions that a few watts will never show up on the other end. the only person that ever knows they are running 40 watts or 20 watts is the guy transmitting.
     
  6. wee electronics

    wee electronics
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    Here's a good link for reference when designing with mosfets to operate in the linear region. Bear in in mind a bipolar transistor is a current in, current out device. The MOSFET is Voltage in, current out device given by equation 1 in app note. The manner in which they are used as finals in an HF radio is open loop. The fact they even work in the application in which they are being used blows my mind. Each to his own. Good conversation guys.

    http://www.digikey.com/en/pdf/m/microsemi-power-products-group/microsemi-make-linear-mode-work
     
  7. Vern torney

    Vern torney
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    Mrf255 or mrf 455 work for me( no 477,520 or FQP13N10)
     
  8. strykerman

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    My stryker 655 keeps popping them every time I run it with my texas star sweet 16 amp. I'm changing to 520's.
     
  9. 9C1Driver

    9C1Driver
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    You might check and see what is causing this or you will just keep smoking 520's too. There might be some kind of a mis match between the radio and Texas Star that needs corrected.
     
    222DBFL, 543_Dallas and psycho like this.
  10. Tim Chambers

    Tim Chambers
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    I would connect the amp output to a 50ohm dummy load, then hook up an antenna analyzer like an MFJ 259B, and see what your input impedance/SWR is. There is often times a trimmer capacitor that can be adjusted inside the amp on the input rail, and trimmed so that the radio see's a good load to transmit into, 50 ohms. Just like transmitting off an antenna with a high SWR, feeding an amp with a high input SWR, you can damage/blow up your finals in the radio.
     
  11. BBB

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    Thinking about doing the FQP13N10 to IRF520 MOSFET conversion on one of my 955s that's down for this all too common issue.

    I would think I should replace all (4) of the 13N10s with the 520s. The Vishay 520 looks to be a drop in replacement... assuming I set the Stryker's pre-drive, drive and final biases at a safe level?
     
  12. Onelasttime

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    I am toying with the idea of taking the Fairchild 13N10's out of my Yeti Optima MKIII and replacing everything with 2 matched 2SC2166's and 2 matched 2SC1969's. Some how we all managed to get by and drive amps etc...with single and dual final radio's with these parts! I have never blown a final in a radio ever but I have never ran a radio that had non-rf mosfets designed for switching power supplies as finals.

    What bother's me is durability and gain. 99.9% on non-rf fet's develop little gain at the voltages we use them at in our CB and export radio's. Most of them need at least 50V before you start to get decent gain from them. I have been into radio since 1991 and never in my life have I seen so many high dollar radio's blowing their finals over and over and over again.

    Fet's or more importantly the non-rf specific fet's that are being used in CB's and Export radio's have almost ZERO tolerance for SWR mismatch and just the slightest mismatch will pop them like Orville Redenkerbocker pop's popcorn! If I need more power than I can realistically expect from a 1 or 2 final radio I will just get a linear amplifier and hook inline.

    I do not understand why people get so caught up in getting a few more crappy watt's out of the radio when it is mindlessly easy to install an external amplifier.

    A poorly terminated pl259 connector or an amp with too much reflect and pop goes the fet's!

    On top of that I am betting people keep turning up the current on the bias which in rf production using fet's is a no no....Pop goes the fet....If you want to turn anything up turn up the voltage. The problem with that is these are being used in 12V car's and power supplies and the rest of the radio is designed around a 12V system. If you want to use cheap crappy fet's and get more power out of them you need to have a separate power source for them. Maybe a DC to DC transformer to get the 14V most of us have in a car up to 48V. Not only would the power go up while allowing the bias current to come down but you would see decent gain!

    There is no free lunch. We should not be using these cheap non-rf specific fet's in these radio's anyways.

    I am sure people have noticed that the watt's these units put out do not seem as though they are getting the same amount of work done in the real world. The radio's do not seem to gain much range for all the added wattage. So their real claim to fame is their low cost and power efficiency.

    When you use a radio with BJT finals in it to drive a linear amplifier you see that these radio's will produce more rms wattage output from the BJT linear but less pep wattage out. On the other hand hook up a radio with non-rf specific fet's in it and you will get far less rms watts out of the amplifier with the same drive input but a lot more pep watts out. This alone should tell anyone even a novice with no understanding of electronics at all that something is different and that all watts are not created equal even if the meter says they are the same!

    I can tell you what the key difference is! Gain....The BJT's have it the fets do not! In fact even with less input power the bjt's will produce more rms.

    If you do not believe me test it out for yourself. Pretty easy to turn the power down so that your fet radio matches you bjt radio for dead key and pep! Watt's with out gain is like horsepower with out torque it is functional useless in the real world but boy do those number's from the dyno ever look impressive!
     

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