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Cobra 29 High Power mod with 2sc1969 transistor

loosecannon

Sr. Member
Mar 9, 2006
4,194
3,587
273
either one will be the same.

those two transistors are basically identical for our purposes.


also remember that you have to quadruple your power output to gain 1 S-unit on someones receiver.

that should tell you how much trouble you should go to for a given power increase.
LC
 

Moleculo

Ham Radio Nerd
Apr 14, 2002
9,043
1,348
283
You have to desolder the coil from the board - remove it. Then you can just unwind one coil off of the can, bend the wire back into original form, and replace it, trimming the excess when done. Remember that the coil wire is coated, so you have to scrape off the coating where you will solder it back on the board. Do that before inserting the coil back into the board.
 

Oldtimer

Active Member
May 20, 2008
223
9
28
74
Stuart Florida
Thanks Moleculo.
It worked great.
My Cobra 25 ltd has the stock final (2078) in it yet.
It dk's 2 and swings to 20.
If I put a 1969 final in would I see much difference or ain't it worth the time.
Thanks again.
 

Moleculo

Ham Radio Nerd
Apr 14, 2002
9,043
1,348
283
You can get the same results from a 25, but you'll have to cross reference the component numbers for the 29 against the schematic for the 25. I don't remember what they are, although I've done it before. Whether or not that's worth it to you is up to you :)
 

jazzsinger

Bullshit Buster
Jul 3, 2008
1,750
333
93
United Kingdom
Me again- go to Grandata Online -they have 14 available as of 30/04/2009 20:40 GMT...At the fantastic price of £1.60...which I think is around $2.30 ? + post & packing....does'nt mention posting to the states...if you have any trouble getting these RF Output transistors either over there or here in the UK let me know and I could send for them here and post them on to you Guys over there in the good old US of A...Noooo problem, just give me a nod...Dave ( Near Manchester,England)

its highly unlikely they are genuine mitsubishi 2sc1969 at that price.genuine ones go for between £10-£15,about 18-30 dollars each.
 

coyote

Member
Aug 1, 2009
1
0
11
52
Moleculo, i want to try your 29 mod w/ 1969 final. i am confused as to what a .2 monolythic is. i think i understand all the other parts mentioned and the procedure was well described. i need only to locate some authentic 1969 and 2166 transistors. there is a ham fest in sept. by me, maybe i can find them there. i am just a little confused with the .2 monolythic part. any help with this would be greatly appreciated.
coyote, 620 in the poconos, pa.
 

loosecannon

Sr. Member
Mar 9, 2006
4,194
3,587
273
a monolythic cap is a type of ceramic capacitor.

it has to do with the way the capacitor is made.

they look similar to tantalum capacitors in shape.

look at an electronics parts store in the ceramic capacitors section, you should find them there.

good luck,
LC
 

rockman

Member
Sep 23, 2009
5
0
11
I just did this mod to an old 29 ltd. A friend game me an IRF530 he said it was the same as the IRF520, and I used the home made biasing circuit instead of the 1230. The radio works, but I am keying like 3 watts and swinging maybe 10 if that. Seems somthing is wrong. Any ideas, is the 530 not the same thing? Any help greatly appreciated.
 

MisterFatty

Poppin Fresh!
Aug 1, 2008
698
34
38
I just did this mod to an old 29 ltd. A friend game me an IRF530 he said it was the same as the IRF520, and I used the home made biasing circuit instead of the 1230. The radio works, but I am keying like 3 watts and swinging maybe 10 if that. Seems somthing is wrong. Any ideas, is the 530 not the same thing? Any help greatly appreciated.


Guess the first question that comes to mind is what meter are you using for measurements?
 
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rockman

Member
Sep 23, 2009
5
0
11
Its a PDC 550. Nothing fancy, but I know it works checked it against two other radios, a stock, that is doing 4 watts and a modded 25 that is swinging 30 watts.
 

MisterFatty

Poppin Fresh!
Aug 1, 2008
698
34
38
I was just looking at a few Spec sheets for various manufacturers IRF-530, they appear to have a fair range capacitance values listed. Do you happen to know specifically who made the one your using?
 

Grey Coyote

Member
Apr 29, 2010
5
2
13
I thought i was following this thread pretty good, but maybe i missed it. A question was asked about which side of band of D11 would you connect the 1k resistor in step number 6. I would like to know that also.

Thanks.
 

Dago 971

Member
Jan 29, 2010
2
0
11
I was asked by a few people how to do this mod, so I figured I'd just post it up.

Please don't copy and paste this mod to other sites/forums, but feel free to link to it.

Also applies to:
Uniden 78
Cobra 25 & Uniden 76 mod is similar, although you'll need to cross reference against the schematic.

1: change the final to a 2sc1969
2: change the driver to a 2sc2314.
3: change the electrolytic capacitor by the audio IC (C42, 1000uf) to a
3300uf, 16v.
4: Take a turn off the output tuning coil (see tuning coil note below)
5: Remove the AMC potentionmeter (VR4), and put a 1K resistor in it's place.
(only two connections are used on this pot, use those two connections
for the resistor)
6: add a 1K in series with D11.
7: Change R48 to a 33K ohm resistor.
8: Change R55 to a 10K 1 watt resistor.
9: change C37, and C68 to a .2 monolythic (this changes the A.F.
response on TX)
10: Now align the radio, start with the output coil, the the predriver
stage for peak output.
11: Tuning notes: Tune L17 for max with audio. Then, tune L23 for max output with audio, this will upset the radio's frequency. So, after L23 is set, adjust L24 to put the radio back on frequency.

Tuning coil note: If the radio says "made in China" on the back, you must remove 1 turn from the output tuning coil with the slug in it. If it doesn't then you may or may not have to. Count the turns, if it has 4, leave it alone, if it has 5, it's too many and won't tune, remove a turn. You may have to add a 68pf capacitor from the left terminal of the coil to ground, with the solder side of the board up. This method produces better results than just removing the tuning slug.

This mod will consistently produce output between 10-12 watts AVG and 45-50 watts peak. If I can find my video clips of Bird 43P power meter and spec analyzer I took after doing this mod, I'll follow up with those.


This looks very similar to a Dave Made Cobra 29 I was able to peek at under the hood. IS this infact his mod or similar to it? I know the Dave Made Cobra 29's are fantastic Shoot Out Radios...
 

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