| Author |
Message |
    
Hotwire
Senior Member
Username: Hotwire
Post Number: 1323
Registered: 1-2005
| | Posted on Monday, May 08, 2006 - 12:48 pm: | 
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Hello guys, A friend of mine who is new to radio just purchased a Cobra 148 GTL just like mine. Yesterday he noticed how the recieve on mine is much more sensitive and quiet than his. Well I figure my antenna (Predator) helps sensitivity but as far as the low noise level I explained that I spent a lot of money to have many inside parts upgraded. Well he is gonna get the 20 dollar tuneup but can't afford the close to 100 dollar upgrades. Our question is, What can we do to his radio internally to get rid of the white noise or at least improve its filtering so the background is silent but signals still come in strong? Then after the mods he will get it tuned. I have heard of the sc2999 mod, I think thats right...will it work for a new 148? anyone have any ideas? |
Bullfrog13x4
Junior Member
Username: Bullfrog13x4
Post Number: 33
Registered: 3-2006
| | Posted on Monday, May 08, 2006 - 5:13 pm: |
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maybe different rec.diods????? the mod you rfered to should work on any radio with that type of chassi with minor variations from radio to radio. you might try tunnimg it slghtly different than the sugested tune up spec.
hope this helps
Bullfrog13x4 |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2825
Registered: 7-2004
| | Posted on Monday, May 08, 2006 - 5:17 pm: |
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2sc2999 
sensitivity or lack thereof could be a result of out of alignment...& i just HATE to have to have a new radio aligned |
Bruce
Senior Member
Username: Bruce
Post Number: 3817
Registered: 9-2003
| | Posted on Monday, May 08, 2006 - 6:35 pm: |
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RETAIL on the 2sc2999 transistor is under 5 bucks it dosnt take 100 bucks to hop up a radio |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1539
Registered: 9-2004
| | Posted on Monday, May 08, 2006 - 6:50 pm: |
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hotwire, just so you dont have to look elsewhere to get the specifics:
the transistors are either labled "Q" or "TR"
not sure which in the new ones.
change TR/Q 14 to 2SC2999 or NTE107.(some people dont like the NTE part but i use one in both my 2000 and 148 and am very satisfied with it)
replace TR/Q 19 with the old TR/Q14.
replace diodes D1,D2 and D34,D35
with 1N6263 diodes.
the NTE equiv. is NTE583
i also use the NTE parts here and am fine with them.
i have to say i might not know what i am missing because i have never tried the other parts, but i noticed a bid improvement after the mods and dont see a reason to change unless someone mailed me the parts for free.
later!
matt |
Yankee
Senior Member
Username: Yankee
Post Number: 1185
Registered: 7-2003
| | Posted on Monday, May 08, 2006 - 8:35 pm: |
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$100.00 worth of upgrades??? I'll bet it not the first model original Cobra 148 GTL. The originals don't need a lot of upgrades, other than the 2SC2999 transistor swap on Q14 and move the transistor that came out of Q14 to Q19. |
Yankee
Senior Member
Username: Yankee
Post Number: 1186
Registered: 7-2003
| | Posted on Monday, May 08, 2006 - 9:40 pm: |
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Second thought, I for one would like to know what the $100.00 upgrades were and why??? I'm serious about this, I'm not poking fun about the $100.00.
Maybe I've missed something here and my Grant XL didn't get something, after the basic mods were done for around $65.00 including the cost of 2 added switches, a few small parts and the hard wired frequency counter.
Carl  |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1328
Registered: 1-2005
| | Posted on Tuesday, May 09, 2006 - 11:54 am: |
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KV, Thanks for the info. I'll save it so when I get the parts I can try my luck at the upgrade. I'm very curious cause I believe my tech has already done this mod to my radio. Need to check the locations you give me.
Yankee, OK maybe I should clarify the exspense better. 80.00 dollars for parts plus labor included. His fee has gone up I think but not sure.
Your correct that it is a new model Cobra 148. If you ever had the chance to examine one of these new cobras fresh out of box with your years of expierence you would immediatly notice how they are made with much cheaper parts and the reciever and transmitter are not up to par.
My tech that I have had the pleasure to befriend for 5 years now has 30 plus years on just Cobra radios exclusively. He loves them cause working on them is like second nature. I was sceptical at first but finally he convinced me saying if I was not happy then no charge. He did many 29's but finally had the chance to do the new 148 and was excited to try his new tune up on a sidebander! I sat next to him at the bench as the shop closed that night watching him work. The radio looked like it was in surgery with leads running here and there, scopes and meters hooked up. Over the next 2 hours I watched as the little pile of cheap components grew. Over 30 major pieces from transistors, diodes, resistors , etc. More componets was added replacements was premium and some was bigger than the older ones. He did a very good job, an expert solderer with the steadiest hands I ever seen. He actually was having fun cracking jokes all the time.
The result was a 148 as close as possible to the 148's of the good ol days, maybe a little better.No echo or beeps and junk just what is needed! Modulation was very strong and superior on SSB. Almost to strong for a 2 pill 1446 amp. I burnt out the modulation LED on the amp! Transmit was screamin! BUT! The recieve was amazing! So qiuet with no white noise at all. With filters off and driving the recieve was nice to hear.Best recieve with it was middle of night at a base 120 miles away and I contacted the base as well! I know of nobody else in my area who could have heard that guy so far away! I still have that radio plus a second he tuned but a little milder for SSB to run my Texas Star! So I have a barefoot and driver radio that guy tuned. They actually have better recievers than my Connex 4800. Not the power the Connex has of course but sound just as good or better in transmit! The tech only does this tune up to Cobra 29's and 148's. The only reason I would ever buy another cobra is if this guy tunes it. Any member who have heard my mobile in DX have heard the 1st model I had tuned. I believe the 2nd model is even better and can't wait for the chance for you guys to hear it in DX soon! So Yankee and some others might be thinking yeah right you got ripped off but I have been into radios a long time also and I can see and hear the difference and I believe it was worth every penny! 73 |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1329
Registered: 1-2005
| | Posted on Tuesday, May 09, 2006 - 12:15 pm: |
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Pat, Have you ever tried a new 148 out of box? To a newbie it may sound just fine but for someone who knows radio and has the refined radio ear then an alighnment is very much needed! My older 148 was 3 kc off. My new 148 was an amazing 9! kc off! 9 kc! How in the world does it leave the factory in that condition? |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2828
Registered: 7-2004
| | Posted on Tuesday, May 09, 2006 - 3:30 pm: |
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i did a new 148 maybe a year & a half ago. 6 months or more later added variable output & a texas star to it. it IS still in an 18 wheel dump truck that drives roughly 500 miles a day. it has not skipped a beat yet. yeah, it looked a bit cheesy inside, with the plastic poentiometers, but then a lot of radios use 'em now. the board appeared 'emptier' then older 148's, but that was because of the use of 1/4 watt resistors where 1/2 watters used to be. this radio never if ever uses SSB, but it was purchased by somebody who understood the typical uniden receiver & wanted that performance. he got it & when i modded/tuned it for him, i was satisfied with overall performance. i don't remember it to be noticeably off frequency. i've heard/touched maybe a dozen new 148's & never noticed any to have anything wrong that needed immediate attention. clarifier not straight up but rcv & xmit being close to the same freq, rcv sensitivity, xmit audio quality-everything 'close enough' to tolerate. |
Yankee
Senior Member
Username: Yankee
Post Number: 1187
Registered: 7-2003
| | Posted on Tuesday, May 09, 2006 - 8:50 pm: |
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Thanks Hotwire,
You still didn't say what was done. But OK.
I like the high quality of the original Uniden sideband rigs. But no, those days are gone forever and we have to keep what we do have of the originals in top condition.
At least you've helped me to more understand why I don't want any of the newer Cobra offerings, the clones of the great radios of yesteryear.
I learned very quickly when I had for a very short time one of the 148 GTL Soundtrackers of China make. Good thing I only had $20.00 invested, even though it was in like new condition and also looked it, had to all but give it away to see it leave my collection.
But that was OK, I used it to pay a $50.00 bench charge for the modification work, on my like new dated November 1979 Realistic TRC-449, (same radio as the daddy of the original Cobra 148 GTL, the Cobra 138 XLR), also I have in my collection a like new Cobra 138 XLR.
Along with the likes of the Cobra 2000 and original 148 GTL, and the Unidens of old like the Grant, Grant XL and LT. The list is much longer of Uniden made radios, those were the real sideband radios of the good old days, when Uniden and Cobra were at the top of the ladder, but alas they are no more. |
Bruce
Senior Member
Username: Bruce
Post Number: 3819
Registered: 9-2003
| | Posted on Wednesday, May 10, 2006 - 6:21 am: |
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hotwire 9 khz? thats almost one channel ! did you meen .9khz ? |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1333
Registered: 1-2005
| | Posted on Wednesday, May 10, 2006 - 11:11 am: |
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Bruce, yeah .9khz
Yankee, Sorry man, All I know is that he very much improved the reciever by what he told me. If I remember right he said that channels would be "tighter" " much less splatter from adjacent channels" "much cleaner and sensitive recieve" " modulation will be increased".
Remember although I have lots of good knowledge of radio I;m no tech by any means. I wish I could look at the radio and tell you what was done but I can't. I'm going to go try see the tech this weekend so maybe I can give some better details later. |
Ironfoof
New member
Username: Ironfoof
Post Number: 5
Registered: 5-2006
| | Posted on Thursday, May 11, 2006 - 8:55 pm: |
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how about adding ferrites to the pos and neg inputs internally My magnum has these and its the quietest and tightest radio Ive ever owned. |
Bruce
Senior Member
Username: Bruce
Post Number: 3828
Registered: 9-2003
| | Posted on Thursday, May 11, 2006 - 10:36 pm: |
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HA?
How would anything on the power lead efect the radio?
To " TIGHTING " up a receiver you must add some kind of filtering in the rf/if chain a channelguard does this.
To increase senistivity you must DECREASE noisfigure of 1st amp stage ( RF PREAMP ) and increase gain.
The 2sc2999 mod does that |
