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QYT KT-980 Plus PA Transistor

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by VK4GAP, Jul 1, 2019.

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  1. VK4GAP

    VK4GAP Ham Member QRZ Page

    Been given one of these with a known issue to use as a Rx'r , works fine too .

    Decided to take a look at it and now having trouble sourcing the PA transistor pictured , it looks like the markings are AFT05MP075W maybe , in the mean-time after removing said magic-less smoke device i inserted a ceramic cap from the output of the driver to the input of the band-pass filters/network (where the output of the final is) and there is around 4W going up the coax .

    Sent QYT a email and looked big-time on the internet , nothing hence this post , anyone see one like that? , its supposedly a 75w vhf / 55w uhf transistor , there are those others that turn up on a search BUT not that style .

    tia & cheers , Paul .

  2. VK4GAP

    VK4GAP Ham Member QRZ Page

    Ok , all can ignore the 1st post , ordered 1 of each after doing some measurements with the vernier calipers , they were cheap enough to experiment with , they fit in there (smaller) , if anyone wants further updates like pcb pics and results or whatever let me know .73

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  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    Where did you find them at ?

    What is the power rating ?

  4. VK4GAP

    VK4GAP Ham Member QRZ Page

    1- On the internet on the Bay with "make a offer listing" .

    2- Same watt as the original 70-55

    3- Yet to see as i ain't got them in my grubby hands as yet , i'll try both , the flange one will be easier to fit as all that will be needed is 2 small larger flat washers on the orig screws although that one might have less gain due to in / out matching differences .

    The other one fits in-between the screw holes going by the vernier calipers so some sort of top bracket/plate across it OR the same larger flat washers needed (i do not know what the underside of that one looks like as yet) , + bit of quality TIM (Thermal Paste ) on both i gather . 73
  5. VK4GAP

    VK4GAP Ham Member QRZ Page

    Ok i do not have the test gear to go any further with this , the RD70 was fine on vhf (60w) , 4 watt on uhf , its the output matching on uhf i reckon .

    Pics show the other one , one has to heat the copper and the other one falls off , no wonder i could not find one like that , clean and prepare the copper and heat it and drop the other one on , simple .

    70w on vhf (turned it back to 60w) uhf only 30w , one has to fiddle with 1 coil specifically to adjust the match but that's all it would develop , as i already mentioned not enough gear to find out .
    cheers Paul .
    btw , QYT actually did respond via email several times .


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  6. KN4WVY

    KN4WVY Ham Member QRZ Page

    Hi VK4GAP, I'll be buying a working QYT KT-980 Plus from a friend for my first mobile radio (I'm a new ham, I'm using a Baofeng UV-5R and UV-82HP for now) and I had a couple questions right along the line of what you were dealing with in replacing the final in your unit.

    I've heard that there are issues with many CCRs (cheap Chinese radios) with poor thermal issues with the finals. In many cases I've read the issue may be little or no thermal paste between the final and the heatsink, and in other cases it may be an underrated transistor that is being overdriven to give a higher output. The QYT KT-980 Plus doesn't so much have the latter issue as the transistor seems correctly sized for 75 VHF/50 UHF watts or so, but I wonder about the thermal paste and heat sink issues.

    I want to better avoid this issue with my unit and I thought I might take the final transistor off or at least lift it up enough to add some high quality thermal paste underneath. I don't think it would hurt, assuming I don't damage the final or board in the process.

    From the first photo above it looks like removing your final involved desoldering at least the upper tab(s) and either desoldering the bottom two or slipping them out of a socket, and removing two screws or bolts that held the copper portion of heat sink from the main board. Does that sound like what you did? Was it fairly straightforward to desolder and remove the transistor or did you have a lot of issues with solder or was the transistor hidden or not easily accessible?

    And maybe most important, did you notice if there were indications that thermal paste or bonding between the transistor and the heat sink(s) / heat sink assembly might have been an issue in your old final's failure? I have heard that some of these units (and CCRs in general) heat up considerably when in heavy use in QSOs. I'm sure they are supposed to heat up some, and a heat sink that remains cold while the rest of the radio warms up (or worst case starts smelling hot) might indicate the heat sink is not properly conducting heat away from the final. Was there any indication that might have been the issue with your unit?

    I hope I don't sound like I'm overthinking here, there isn't anything wrong now with the unit I'm considering buying but I was told (and saw) that the heat sink wasn't heating up much at all with a moderate use test I watched. That may not indicate anything wrong but at least I'd like to touch the final transistor (after turning off the power) after a QSO test I'll run to see if it heats up at all and if the heat sink material adjacent to it heats up along with it.

    Thanks for your insight and experience on this!
  7. KN4WVY

    KN4WVY Ham Member QRZ Page

  8. K7AEK

    K7AEK Ham Member QRZ Page

    Well, did it work? I'm in the same boat with a 980 plus with blown finals. I ordered another mosfet based on that part number.

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