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MOSFET conversions for upD858 and MB8719 boards

Discussion in 'General CB Services Discussion' started by ExitThirteen, Mar 10, 2011.

  1. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    It's no problem. I'm all about keeping the old school radios up and going. Hopefully, this will keep some interest and involvement in tech work and repair of the older rigs. We need to keep CB alive as best as we can. (y)




    ~Cheers~
     

  2. Onelasttime

    Onelasttime Well-Known Member

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    Yes I think plenty of people are all for parts swaps to replace obsolete parts no longer made. I think the problem is 2 fold. 1) People are taking out perfectly working finals and drivers in the quest for a few more meaningless watts. 2) Second if the part is still available and and you have a collector rig why not keep it all original $16 is not a significant sum for a final that will last another 20+ years. When the parts are gone completely or they get crazy like $30-$100 per part it would make more sense. If the original part lasted 30+ years why not replace it with an identical part.

    Nothing is much worse than idiots butchering up a radio in the pursuit of a few more meaningless watts especially when the old parts in the radio are working as they should!
     
    AudioShockwav likes this.
  3. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    ... and NOTHING is worse than the person that criticizes other people for doing something different to their radio, from mics to receive mods to MOSFET mods. You don't have to do any of these mods if you don't want to. No one is forcing you to do anything.

    This thread is for information and educational purposes.

    If you can't say something nice, don't say anything at all.


    ~Cheers~
     
    walterjn, NZ8N, Tallman and 2 others like this.
  4. Onelasttime

    Onelasttime Well-Known Member

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    Saying something nice that is not at all true is just a pretty lie and does no one any good!

    If someone needs a safe zone or a crying closet that is their problem not mine.

    Yes, it is perfectly alright to criticize! In fact, if more people spoke the truth openly we would not have half of the problems we have. What do you think keeps incompetent people in the workplace. If people had spoken openly about things the housing bubble could have been averted, General Motors and the UAW would not have needed a bailout and neither would the banking industry.NAFTA would never have gone through either. Half truths outright lies freq the lie of omission and people keeping their mouth shut to either avoid any responsibility, keep riding the gravy train at the cost of the nation or under the false notion that it would be impolite to point out the obvious.

    The messes that Europe and the USA is in socially, politically, economically is the direct result of otherwise good people keeping there mouth shut when they see other people either acting like fools, committing criminals acts or doing otherwise unwise things.

    People are keen on looking like the Scholarly Professor or the Wise Old Sage but they never worry about doing the responsible thing since they will never take any blame for someone butchering their radio. They sing the praises of a mod but never the unfortunate truth that also comes with most of these mods which manifests in some unwanted not at all positive side effects.


    No amount of Mosfet swapping for BJT's inside of a radio one for one has ever produced enough of an increase in power to be worthwhile at the other end of the signal. The only thing these mods do reliably in the hands of a novice is create more problems.

    So instead of $15 lets say to replace a defective part you are spending $0.50 to $1. Never mind that durability is always a problem with these non-rf-specific fet's. Even OEM's that use them can not get them to last much past the warranty period and it really gets bad when golden screw drives come out!

    You never point out the obvious to anyone about these mods ever!!!! Spin things to only talk about positives. You know nicotine has some fantastic effects on memory, cognitive performance, hand-eye coordination, short-term productivity helps to alleviate a lot of symptoms in various mental health conditions and disease states. If that is all someone told you about nicotine with no historical perspective on it's delivery systems, addiction, short term and long term cost both directly and in terms of medical cost's you might think nicotine was some incredible medical drug that everyone should use! Same thing with Mosfet Conversions they sound great the way you and other's spin it but if you actually presented all of the facts truthfully and balanced few would do it unless they had no choice.

    No one is saying people should not have a choice! I am not saying people should not have a choice. What I am saying is all of the stuff you and everyone else that pushes these mod's leaves out and fail to mention. When people make a decision they should have all of the facts not 1/2 of them! If something is stupid only a fool, a thief or someone that hates their fellow man would fail to speak the truth!

    You clearly have an agenda that you are pushing and it is not without it's obvious bias. Maybe you do not mean to be deceptive I have no reason to think you are being purposefully deceptive but you and everyone else that pushes the MOSFET conversion always neglect to tell people all of the facts.

    If something can not stand up to the scrutiny of other's than it is normally not a good thing.
     
  5. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Holy cow. What just happened?
    I for one am truly grateful for all the help and knowledge given freely on this site.
    Having something nice to say is not about telling a pretty lie. It is about having good manners and respect for all involved. People can express any opinion this way. If someone wants to pay $16 for a part then that's up to them. That doesn't mean that finding a way to use a cheaper part is bad and anyone doing them is a hack. Being able to modify a radio is what attracts me and a lot of people to this hobby. No I am not going to rip the final out of my Madison but I do find this conversion interesting and good to know in case I need it.
     
  6. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Mind if I chime in...?

    Has anyone read the bottom of the page?

    Lestweforget.jpg

    I look at this as a someone has granted us a privilege to express our rights.

    We still need to respect others rights.

    :+> Andy <+:
    (...well, if this boots me off - well I fought for ya'...)
     
    Chipper, Dmans and Shadetree Mechanic like this.
  7. Harley3315

    Harley3315 Active Member

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    Old being brought back from the dead but what about a mod fopr say am only pll02a radio like the Ge. 3-5812a?
     
  8. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    You missed the entire intent of ExitThirteens post. Yes the parts are still available at this time, but for how long?
    I applaud any technician or engineer who would take the time to design this to keep old equipment working.
     
    #128 Tallman, Oct 25, 2019
    Last edited: Oct 25, 2019
  9. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    It is not a right to be a member of this site, it is a privilege. And as a privilege it can be revoked at any any time. The frame you high lighted is not the constitution. We are here at will of the moderators and the board owners.
     
    Harley3315 likes this.
  10. kopcicle

    kopcicle Sr. Member

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    There are a few things other than output transistor failure that will make a radio fail to transmit.

    Try listening with a nearby radio first. Check the receive and check the pll for lock. If the PA and the receiver work , if it has voltage to the final and can be heard by a near by receiver...


    Yes , the above modifications will work for the 3-5821a. If you're up against a steep learning curve just let us know.

    To get started post the board #
    "PTBM***AOX or COX . It will help get the correct schematic.
     
  11. Harley3315

    Harley3315 Active Member

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    It's the ptbm050c0x it's not a part failure it's a want to upgrade the current 1306 that's in there now and the c1846 isn't likely to get 20 watts out put.
     
  12. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Harley3315 likes this.
  13. Harley3315

    Harley3315 Active Member

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    I'm well aware of rfx75 and stingers and such this is how I want to do it just enough to get 20-25 watts the mosfet should do the trick just fine this is only for my shop radio on a dipole antenna for about 10 blocks range.
     
  14. nomadradio

    nomadradio Analog Retentive

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    It's all about the objective.

    If what you want to accomplish is an efficient, economical and reliable repair that's one scenario.

    And if you just want to experiment on an old radio with little market value, that's a perfectly-valid objective, too.

    I'll suggest that all the components that have the driver/final supply current passing through them will be working harder. The switchmode MOSFET transistors adopted by the radio manufacturers are not being used in new radios because they work well to amplify RF. They are being built into the radios because they are irresistibly cheap, and because they are available in any mass quantity you want.

    Period.

    They are less efficient, but not enough to make the radio blow up during the warranty period as a rule.

    "Less efficient" translates to more power supply capacity. The power supply built into a base radio just won't be up to it. A mobile radio is not crippled this way, so you'll only need to worry about the additional current through the AM modulator circuits for the most part.

    The older bipolar parts were designed to be efficient and rugged (mostly) RF amplifiers with a lot of gain and the minimum power-supply requirements. But they were all discontinued around 2007 or before. Never mind why. Not in the mood for that rant right now.

    Most any CB built with a bipolar driver/final can probably be adapted to the dirt-cheap switchmode MOSFET transistors like the IRF520, FQP13N10 and such. Unless you are starting with a step-by-step procedure that shows all the component changes, you will be working out those details for yourself.

    The input side of the driver circuit and final circuit will require the biggest redesign. Adapting the setup and component values shown on the web for popular radios like the Cobra 29 and 148-type radios will be the easiest starting point. How much you'll need to adapt the setup shown for those radios to your radio is anybody's guess.

    Only one way to find out.

    73
     
  15. Robalo

    Robalo Well-Known Member

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    i been here for long time with few likes and cb is my hobby and my passion. and poor and technical comments.
     

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