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2sb817 upgrade? Dual final 959 needs a better regulator.

Discussion in 'Amateur Radio Modifications' started by Alex Faught, Mar 24, 2017.

  1. Alex Faught

    Alex Faught Member

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    Is there a suitable replacement for the 2sb817 that Is capable of handling more current? I have a galaxy 959 with dual 13n10s with a 13n10 as a driver. It is doing 55 pep, I put a 2sb817 in it, but even it gets pretty warm. Is there a suitable replacement capable of more? Any help would be appreciated. Thanks!! alex


     

  2. Alex Faught

    Alex Faught Member

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    Correction, I have a tip36c in it and am looking for something even more capable than it.
     
  3. sp5it

    sp5it Master of puppets

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    BD250C, but I would do npc-rc and rwob mod and no problems with weak regulator transistor.
    Mike
     
    LeapFrog likes this.
  4. JoeDirt

    JoeDirt Well-Known Member

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    Its fine if it gets warm or even hot. I have dual IRF520's in my 959 and it will burn you. Been like that for 8 years or so.

    You could always "volt" the finals to take the current load off.
     
  5. Ranch55

    Ranch55 Active Member

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    Palomar Max Mod ....... see description below. You will need to drill a new mounting hole in chassis ........

    https://www.palomarelectronics.com/product-page/palomar-max-mod

    I purchased my Max Mods from here ......About 3 week delivery ......

     
    Shadetree Mechanic likes this.
  6. Robb

    Robb Yup

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    If you are getting the AM Reg too warm; then it is from two causes. One, you stay keyed up for too long. Second, you have the mic gain to high at the same time. The AM Reg doesn't care if you have four MOSFET finals or one; it's job is dealing with mic audio.

    You do NOT need to do the RWOB mod. Peaking the TX coils has always been enough in every Galaxy radio I've ever worked on.

    Also make sure your AM Limiter transistor is also in place, as this will also help keep your AM Reg cooler. Removing the limiter and then using the radio in SSB mode will also tell everyone out there that you don't know what you are doing, simply because it will make you audio no better than awful or worse.

    You can upgrade your 817; but if the radio is running OK after replacing the limiter I wouldn't do that.
     
  7. Ranch55

    Ranch55 Active Member

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    I have found the 2SB817 to be plenty adequate, but the Palomar Max Mod upgrade component will definitely operate cooler........
    And, I am in not as knowledgeable as the above poster ......
     
  8. sp5it

    sp5it Master of puppets

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    Above poster is not knowledgeable as it seems.
    That transistor is getting hot, because all current going to driver and final(s) is passing through.
    So, if some butcher is peaking and tuning radio, raise carrier, more current flows. More current, more heat. Simple as *uck.
    The point is, that AM regulator must be capable to pass that current. End of story.
    Mike
     
  9. bob85

    bob85 Supporting Member

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    Robb
    The AM reg/mod transistor does care how many finals you have, its is the dc power supply for the driver & finals, the clue is in the name, AM regulator modulator,

    more finals = more current that the transistor has to supply.
    the mic audio just swings that supply up and down,

    when you key the transistor is dissipating the voltage dropped through the transistor x pa current as heat,
    that's why older single final exports could get away with using a smaller AM reg/mod transistor,
    dual final rigs had AM reg/mod circuits with more than twice the current capacity.
     
  10. Robb

    Robb Yup

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    Yes; you are right. And so is sp5it. I was trying to point to the AM Limiter action upon the AM Reg. Galaxy said that the #1 failure of that regulator was due to over-modulation and limiter removal directly. We had one of the guys from Galaxy warranty repair get on the forum awhile back and state as much, as I'm sure you remember. They were seeing this failure often, even with a single bipolar final radio. My mistake for creating this issue for the way I wrote it.

    Alex Faught:
    The other mod to that circuit is to also upgrade the companion part to Q54, which is Q55. Check and see if Q39 has been removed. If so; then replace it with a 2SC945 - common and cheap as chips.

    http://www.cbtricks.com/radios/galaxy/dx959/graphics/dx959_ept069610z.gif
     
    #10 Robb, Sep 18, 2017
    Last edited: Sep 18, 2017
    bob85 likes this.
  11. loosecannon

    loosecannon Sr. Member

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    one thing i have not seen mentioned yet is that the package size will be the same, meaning that the surface area on the back of whatever transistor you choose will be the same, as will the size of the "heatsink (chassis)" that it is attached to.

    I don't think upgrading to a higher current rated part will produce the desired effect IE running cooler than the other part.

    the only difference between the two parts are the junctions inside, and if the old transistor pulled 7 amps, and was able to dissipate a certain amount of heat, why would a part with larger junctions, still pulling 7 amps through it be any cooler?

    This is a question that is a bit above my pay grade, but i will say that it's not easily answered with a google search.

    I spoke with a co-worker of mine who is currently taking a CMOS class and going for his EE degree, and while he wasn't 100% sure, we both seemed of the same mindset that the higher rated part would still get to about the same temperature as the lower rated part, all other things being equal.

    maybe one of our resident gurus can give a ruling on this?
    LC
     
  12. nomadradio

    nomadradio Analog Retentive

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    It's called "thermal resistance". Described as so many degrees per Watt. The thermal "circuit" here starts from the silicon die to the metal surface of the transistor's tab. From there to the heat sink. And from the heat sink surface to the air around it.

    Smaller surface in contact with the heat sink has higher thermal resistance. Instead of the voltage drop you see pulling current through a resistor, you see a temperature drop from the silicon die inside to the metal surface on the rear, another "resistor" from the transistor's metal surface to the heat sink (side rail) surface. The transistor's silicon die generally melts above 150 degrees C. The intent of the heat sink setup is to keep the silicon die inside the transistor below the danger temp.

    A transistor with a larger metal surface in contact with the heat sink should, in theory, run cooler at the same wattage as a transistor with a smaller contact surface.

    But the heat sink still has the same heat energy being dumped into it. Won't make it any cooler at all.

    For anyone who dogs the radio hard enough to worry about heat, the RWOB (Red Wire On Bottom) trick cures this, but just moves the weak link in the chain. Doesn't make it go away.

    73
     
    Shadetree Mechanic likes this.
  13. loosecannon

    loosecannon Sr. Member

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    Nomad,

    while i understand your lesson here, i'm not sure if i actually saw an answer to whether or not a higher current rated part in the same package would run cooler than a lower rated part with the same current running through it.

    for example, 7 amps flowing through a TO-247 transistor that is rated for 8 amps, and attached to the side rail of a mobile chassis will achieve a certain operating temp.

    will that operating temp. be less if a 15 amp rated TO-247 is used in its place with the same 7 amps running through it?


    If you did answer this, i missed it.
    LC
     
  14. loosecannon

    loosecannon Sr. Member

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    well we got a ruling from an EE professor, and he said that the larger rated device will get the heat from the silicon to the metal on the back of the transistor more efficiently, which will keep the junctions under the volatile temperature.
    But, the same amount of current is being run through the device, which means that the heat getting from the back side of the transistor to the heatsink will be the same as the lower rated part in the same package.

    he said this could equate to the heatsink itself actually getting a bit warmer with the higher current rated part, since the heat is being moved out of the device at a faster rate.

    the transistor itself might run a bit cooler (hardly noticeable i am told) but the heatsink will reach the same, if not a little higher of a temperature under the same operating conditions.


    so, it would seem that the answer is no, changing to a higher current rated part in the same package will not produce a cooler running radio, all other things being equal.
    LC
     
  15. Onelasttime

    Onelasttime Well-Known Member

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    I got an answer even an idiot can understand. We are talking Fred Flinstone and Barney Rubble can get. Put the radio back to stock. Give it a proper alignment and the heat issue will go away. If you upgrade the parts but keep the power at OEM levels than you should get more durability. Unfortunately, people always want to stick bigger parts in and crank things up! If you need more power get a linear amplifier bjt, LDMOS or tube your choice.
     

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