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Message |
    
Rumblefish
Junior Member
Username: Rumblefish
Post Number: 37
Registered: 12-2002
| | Posted on Friday, April 27, 2007 - 4:55 pm: | 
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I'm attempting the rx mod for this radio. I was informed the first rf amp on this radio is tr-1 which is a 2sc945. I was also informed that the am detector diodes are d-13 ,d-14 and d-15.this just doesn't seem right. im thinking the 2sc 2999 should go in tr-5. the detector diodes look like d10 and d11. is this right or am i off in left field?? I'd like to replace the rf amp and the noise blanker diodes and the am detector doides with the nte 583 diodes and the 2sc2999 transistor in the proper spot. the info i received on another web site has me confused?? any help would surely be appreciated. thanks steve |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2511
Registered: 9-2004
| | Posted on Saturday, April 28, 2007 - 10:50 pm: |
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still messing with that 139xlr are we? LOL
i think i gave you just enough info to destroy that radio if you tried hard enough.LOL
glad to see its still up and running!
anyway,
sorry, the 2999 mod may not work on this radio. well, that is to say, that it doesnt use the same RF amp transistor as the rest of the radios that accept this mod do. (2SC1674)
the 139xlr chassis uses a 2SC1730, which, if you look at the SAMS, uses an ECG107 as a sub.
now, we know that ECG and NTE numbers are the same, so that says that the 2SC1730 can be replaced by an NTE107.
what happens if you go to NTE's cross referrence page and type in 2SC1674?
yep, NTE107 pops up as the sub.
so, the 2SC2999 will "work" as a sub, but whether or not it will show an improvement to the noise floor; i dont know.
if you do it; please post the results!
its TR5 that you want to replace with a 2SC2999, NOT TR1!
as for the diodes, its D1, and D2 for the AM detector diodes, and D21, and D22 for the NB diodes.
replacing these with 1N6263's (NTE583) should work just fine!
havent done it myself, but it should show the same improvements it shows in other chassis.
best of luck,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Rumblefish
Junior Member
Username: Rumblefish
Post Number: 38
Registered: 12-2002
| | Posted on Sunday, April 29, 2007 - 8:18 am: |
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I replaced the 2sc1730 with the 2sc2999. noticed an improvement of 1 s unit and a much cleaner sounding receive. fringe stations that were unreadable are now out of the noise level. very nice improvement indeed. seems even the 2sc1674 was an improvement over the 2sc1730! as for the diodes, looks like d1,d2,d21 and d22 are the 142gtl diodes. anyway tr5 replacement in the 139xlr is a worthwhile upgrade. thanks again for the help.3's and 8's steve |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2515
Registered: 9-2004
| | Posted on Sunday, April 29, 2007 - 11:26 pm: |
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D1,D2,D21, and D22 ARE the correct diodes to change in the 139XLR.
i checked the schem to get them.
just a coincidence that they are the same in the 142gtl.
the reason its always D1 and D2, and then some D number in the 20's or 30's is because all radios follow basically the same design for schematic layout, and that is how the part numbers are determined.
im going to try using a 2999 in my 139xlr.
thanks for the tip!
in mine, im going to change R43 back to 680K to see what the effect for the average user will be.
let me know how much the diodes help.
BTW, DONT adjust the noise blanker coils without the proper scope/analyzer setup.
in this chassis, you can cripple the receiver by misadjusting them.
have fun,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Rumblefish
Junior Member
Username: Rumblefish
Post Number: 39
Registered: 12-2002
| | Posted on Tuesday, May 01, 2007 - 9:14 am: |
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hey kid, I dont know if we're looking at the same schematic. on my 139xlr d21 and d22 are limiting diodes in the mic amp circuit. If you look at the mods copper has for the 139xlr, you'll see d21 and d22 are to be lifted and a 4.7k put in. d1 and d2 appear to be input diodes for the rf amp. I believe the ones that need to be replaced are the bigger 1n60 general purpose diodes. d10 and d11 are used as detector diodes as well as d15 and d16. d1 and d2 in the 142gtl as well as d21 and d22 are 1n60's. please recheck the schematic and compare the two. I hope we can get this resolved. thanks steve |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2525
Registered: 9-2004
| | Posted on Sunday, May 06, 2007 - 10:46 pm: |
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sure, i'll look again and post back.
might take a day or so...
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2526
Registered: 9-2004
| | Posted on Sunday, May 06, 2007 - 11:20 pm: |
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wow!
so sorry for the misinformation rumblefish!
not only am i looking at the wrong schematic; i also was looking at the wrong type of diodes thinking they were subs for 1N60's. DOH!!!
thanks for bringing this to my attention, as i have had this schem. incorrectly labled 139xlr on my harddrive for some time now.
how did i forget about D21 and 22?!!!
i've only done that audio mod about 20 times!
(one guy wanted me to use a jumper instead of the 4.7K. to each his own.LOL)
D10, D11, D15, and D16 are the only 1N60's that i can find that might have anything to do with AM detection.
the noise blanker may not use them in the same way that other radios do.
i will tell you that you should be able to replace ANY 1N60 diode with the 1N6263 (NTE583) and it will work.
you wont break your radio trying it.
i dont have the right schem. so i am just looking at a 138XLR to get the info.
i have not done these mods to this chassis.
if it were my radio, i would replace D10 and 11, see if there is an improvement, then replace D15 and 16, and see if there is further improvement.
again, sorry about the mix up.good eyes!
hope this helps,
matt
PS-let me know how it works, i might want to try it myself!
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Rumblefish
Junior Member
Username: Rumblefish
Post Number: 40
Registered: 12-2002
| | Posted on Friday, May 11, 2007 - 7:29 am: |
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hey matt, glad we got that one figured out!!! well,so far the rf amp upgrade is very worthwhile.the diode upgrade seemed to "smooth" out much of the static coming in. Seems our 139xlr's have an excellent noise blanker already.The diode improvement isn't as noticeable as in the galaxy and rci boards. the 2sc2999 is a very noticeable improvement over stock. the old 139xlr is still running super strong. 30 years old, still kickin butt and taken names!!!! LOL. steve |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2529
Registered: 9-2004
| | Posted on Sunday, May 13, 2007 - 3:18 am: |
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awesome,
you have inspired me to do this to mine.
thanks, and best of luck with that radio.
maybe i'll get to hear you one of these days on the CEF net.
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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