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adding second final to a 939

Discussion in 'CB and Export Equipment and Accessories' started by 43315, May 13, 2009.

  1. 43315

    43315 Member

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    Has any one come across plans for adding the second final irf 520.
    I can find the plans for the 1969 finals but its how to change it to a mosfet.



    The 939 has one 520 in it and not sure what I need to add to put one more in.
    I drive a company truck and they got a little hot when they saw my amp so it had to go.:sad: The 939 is the same board as the 949 etc. AM only, I'm getting about 15 to 18 out of it now whats a good guess if I add one more 520? I would be happy with a clean 30 or 35 watts.
     

  2. Moleculo

    Moleculo Administrator
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  3. 43315

    43315 Member

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    Yep its the same board, That one is the one where its going from a 1969 to a 2030, I'm afraid I would be taking things out or adding that I don't need to as its already has a 520 in the first slot.
     
  4. Robb

    Robb Yup

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    To put the 1969 finals in it, you would have to change a bunch of parts for the conversion. It would be easier to put in another ERF2030 - and cheaper too. Not to mention, that you will be getting out about 5-10 watts more PEP. Or put in two IRF520N's at $1/ea. The 1969 are $10/ea.

    If it was my radio, and I wasn't going to run it into a low-drive amp, I would go with the IRF520N's and see even more output. Could be as much as 20 watts more PEP. They are direct replacements for the ERF2030. Cheaper - too. Just get a few when you order them, and insist on them sending them to you in an anti-static bag. MOSFETS are prectically indestructible while on a board. They will burn or break if abused or not biased correctly. Their one true weakness is getting destroyed by weak static charges when being incorrectly handled or shipped. Same is true of the ERF2030's...
     
  5. dxhound

    dxhound Active Member

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    Just buy an rfx 75 to replace the finals and get a good 100 watts for $35!!
     
  6. Moleculo

    Moleculo Administrator
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    I would seriously consider that before doing a second final mod. It's probably about the same amount of work, and your company will never be the wiser, since it just ends up looking like a stock radio with a heatsink. Here's one place you can get them: ;) Worldwide Radio Forum Store
     
  7. 43315

    43315 Member

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    good call, thanks
     
  8. 9C1Driver

    9C1Driver Sr. Member

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    I would try a tune first, even with one 520 final you should be way above 15-18 watts. If I remember right those 939's stock should tune to 30-35 watts. I would contact one of these places and discuss your options on the phone.

    Custom CB Radios, We build what others only dream about. From Cobra to Galaxy to Connex . We Also carry a full line of accessories for all your CB Radio Needs.

    Sparkys CB Shack is your 1 Stop Source for CB & 10 Meter Radio Sales & Service
     
  9. Cityboy

    Cityboy Active Member

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    9C1DRIVER I have done several of the newer mosfet radios and have not seen 30-35w peak; but that was without clipping any limiters or modifying the radio beyond a peak and tune and most importantly I ran the radio right at 13.79-80v on my Astron vs-35m during the peak and tune. This is what I ususally see out of the single mosfet radios Ranger 396,966 Galaxy 949,959 is a deadkey = 7-9w, and PEP of 24-28w max with modulation set point at or around 50-62% and swings to 100%. 43315 you should be seeing more than what you are getting so something has not been done, it sounds like the modulation hasn't been turned up and only the power has been. What is your deadkey and then we can tell you where to go from their. The RFX-75 is a very nice addition to the radio, but remember you will totally lose your warranty if this is new and if you install the RFX-75 and it is doa when you install, powerband the manufacture of the RFX will not cover it. The reason being is that they are not intended for the use on this radio but for the final transistor replacement on Magnum radios and you have to modify the RFX-75 to work on yours and cut wires. This will automatically drop the warranty on the Radio and RFX; but it is your call. I have done this to a cobra 29 chrome special edition and never got the numbers that they talk about and I have several other friends that installed them and got very similiar numbers that I did. If you run 13.79-80v supply into the radio you will see similiar numbers to this if installed correctly. Deadkey about 14-15w, the PEP was 75-78w. I was pretty satisfied with these numbers, but was baffled why others were getting bigger numbers and basically I believe boiled down 2 things. 1. The supply voltage was much higher that 13.80v say around 14.4-15.0v, if you ask the shops what supply voltage they use when testing they may all have different numbers.2. Spreading the coils on the RFX-75 before installing could raise the numbers. Be aware you will need all the equipment to re-allign the TX and RX when you put RFX on; and I know that Sparkys when he installs does a good job and charges I believe around $75-100 including the unit you just have to ship to him. I think he will get somewhere around 12-14w dk, 90-95w PEP and that is a ballpark value because I don't know what he runs his power supply at. Well that more than enough you make the call.
     
  10. The Jerk

    The Jerk Active Member

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    I looked into this mod for a 959, and was told it wasn't worth the money or time to complete. It was also indicated to me that the radio would suffer on SSB if not done right, if that's any concern.

    I would like to have the extra final to push my 4-pill, but I'll leave well enough alone.
     
  11. Cityboy

    Cityboy Active Member

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    The Jerk you are correct in that it may suffer on SSB and Powerband is coming out with one that is SSB compatible, or they have already done so. Check around with Al at Sparkys about this. As far as it being worth it, it is a matter of opinion and price. If you buy a refurbished 959 from Sparky and have the RFX installed and shipped to you it would cost around $119 for radio + $75 for the RFX and $12 to ship with a total cost around $206 approximately for a radio that will key up around 12-14w dk and swing to around 95 or so. This amount is approximate so talk to Al for the full price and the effect on the SSB and if powerband has come out with the new one. For the price and features of the 959 plus the power unless you are a true SSB user and you are a truck driver with limitations on amplifiers this is the way to go. Good luck.
     
  12. 43315

    43315 Member

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    939 is am only.
     
  13. Cityboy

    Cityboy Active Member

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    You are correct in that the 939 is an am radio only and that is the one you are talking about; but THE_JERK was talking about the 959 and is a much better radio than the 939 and for the price I gave you is well worth the price.
     
  14. The Jerk

    The Jerk Active Member

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    I was also speaking of adding a second FINAL, not the little deal you are speaking of...adding a second final supposedly won't provide significant improvements, and SSB suffers.
     
  15. Cityboy

    Cityboy Active Member

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    The Jerk they have already come out with a SSB friendly unit from RFX and Cbrepairman has them and charges several more dollars for the complete install. I am sure you could probably check around and order one from Copper electronics, Sparky's, or such. Then you have all the power plus the SSB will not suffer; but if you install you will need to have the necessary equipment to align all sections of the radio as be very familiar with re-aligning the SSB section of the radio.
     

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