President Lincoln

[KZ810Rider]

I have the above radio with a MRF 455 final. Problem is 2 years ago I put the radio on the shelf in working condition, and now it doesn't work. Turns out the final crapped out. My question is how hard would it be to swap in a 2sc2290, or maybe even a 2sc2879? Everything else checks out OK, and I figured since I'm replacing the final why not go one step further. Thanks.


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[KZ810Rider]

I have the above radio with a MRF 455 final. Problem is 2 years ago I put the radio on the shelf in working condition, and now it doesn't work. Turns out the final crapped out. My question is how hard would it be to swap in a 2sc2290, or maybe even a 2sc2879? Everything else checks out OK, and I figured since I'm replacing the final why not go one step further. Thanks.


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[Moleculo]

I sent Docs a 2510 a while back with a 1446 in it that worked "OK" but the mod wasn't done by the books. It was doing about 20 watts AM. I asked him if he knew how to fix it properly, he said no. Personally, I'd just replace the final that's in there. Now, I'm not a tech, but the trouble you have to go through to get any real gain figures from changing to one of those other transistors is going to be a lot of work. I mean if you can excite those pills.....





Moleculo




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[Moleculo]

I sent Docs a 2510 a while back with a 1446 in it that worked "OK" but the mod wasn't done by the books. It was doing about 20 watts AM. I asked him if he knew how to fix it properly, he said no. Personally, I'd just replace the final that's in there. Now, I'm not a tech, but the trouble you have to go through to get any real gain figures from changing to one of those other transistors is going to be a lot of work. I mean if you can excite those pills.....





Moleculo




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[ElectronTubesRule]

Well just because the case matches up SOT 123 does not mean the leads are in the same orientation. That is the obvious.

I have not had to do this but years ago when the MRF-455 price jumped sky high and such I looked into this. The fact that you are gettign 20watt's is a pretty good sign. What you need to do now is make sure resistors and diodes in the area are up to scratch for any difference in current potential and you need to re-bias everything for that final. If the bias is still set for the MRF 455 and it is different then the SD1446 I would not expect to see great performance..... It would be no different then tossing in 2312 in place of a 1969 and wondering way watts are done and swing isnot right etc.......Even when you put a stock part back in as in OEM replacement you have to rebias things normally.

If you look at what the OEM did to put the MRF 455 in place of the MRF 477 you have to pretty much do such the same only in this case I would imagine you will not need to change the circuit's involved just swap out some small parts ie diodes and resistors. I wuld imagine the pre driver and driver used to drive the MRF455 is also enough to drive the SD1446.

Go back and review the initial power mod that people where doing before the MR477 became insane to get a hold of then look at what the factor did when they added the MRF 455. Just reviewing those intital mod's should allow you to figure out what is out of whack and what needs to be changed in the SD1446 mod you have done.

Do not try to get the full power of the SD 1446 out of this chassis it is not going to happen you will damage the board. I would limit output on SSB to not more then 60-65watts when you have the RF Power turned up all the way up assuming yours will do this cleanly. I would set AM to 30-45 watts tops then leave the RF PWR at 12 o'Clock and let it swing Should give you a 12-15 watt dead key swinging to 30+. I am going from memory but I know mine was meter bender for it's time. Any more then that and you need to just invest in an external amplifier and go that route. This radio is tightly packaged and all that heat has to go some place why heat soak your parts for little gain.

I might have a line on some good replacment transistors but I have not tried them out yet. Be even better to just put your radio back closer to stock and get an external amp!