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Volting a Cobra 148 GTL final?

Couldn't agree more! When i first started in the radio hobby I had a 148 and did every mod in the book to it, I talked on it for a year or so. Few years later i started having problems with the same radio, i probably spent a month trying to figure out what mods i did to return it back to stock.

148/2000/Grants are great radios out of the box, and ExitThirteen we just need to make sure people know not to pull TR24 :eek: or install a swing kit/NPC mod.

Don't get me wrong swing kits have there place but not in a 148/2000
 
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now i see what you were referring to ExitThirteen.

and you are absolutely correct also. anyone wanna make an MB8719 chassis sound like crap on SSB, and make the mic squeal on AM?
by all means remove the AMC transistor. LOL

i too have tried pretty much all of the mods ever invented for this chassis, and many are not necessarily improvements in my opinion.

i do like the cap changes that motormouth maul published on his site a while back. they are for the frequency response curve of the receive audio.

the schottky diodes mod is a really good one on this chassis, and doing the AGC diode with it is even better, USUALLY. i say that because i did it to my madison, and it did not seem to like it. it acted funny is the easiest way to put it.

i actually like the sound of the NPC mod using the 10uF cap, with R131 removed, but i run my dynamike at about 1 or 2 o'clock, and i use an RK56 mic with it. try this mod with a power mic and P U. (IMO of course)
i should mention that i do the R114/ C46 mod in addition to this.

very important for good SSB audio in these radios is proper biasing of the driver and final. i have done 30 and 60, 40 and 80, 50 and 100, and i really didnt see too much difference in the audio quality, which leads me to believe that the final being double the driver is more important than the actual number, within reason of course.
also never turn the ALC all the way up. turn it up till the meter stops moving upwards, and then back it off a smidge.
as long as the AMC transistor is still in the radio, and not messed with, the SSB audio will be awesome.


i realize that most participating in this thread already know all these mods well, but maybe havent tried certain combinations.
the ones i listed above are the ones i currently do to my personal radios, and i am more than happy with the results.
LC
 
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One should keep in mind that it is nearly impossible to high level modulate a transmitter to 100% when you only apply modulation to a single stage within the transmitter. This type of AM requires that you modulate two stages to achieve full audio. When you tie the collector of the final directly to the 12 volt DC line, you stop this stage from being modulated. It is much more effective to modulate the 12 volt line before feeding the final, using transformer coupling or capacitor coupling with a choke to prevent the DC line from loading down the AF audio.
 
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137 said:
I guess if you live that close or are in close quarters at all times maybe it matters, for me it doesn't. Some of it to is personal preference, some like soft jazzy like guitars while some like the distortion of rock guitar, don't get caught up in thinking your way is the only way. I personally have never had one complaint in over 20yrs of radio, yet I find nothing but trouble with your types on the internet, always assuming that I must be awful to deal with in person, like my station must be total trash... Funny, I never seem to hear that from anyone I actually TALK to.
Click to expand...

The people you TALK to on CB bands do not know what a clean signal is 90% of the time. They are entirely unaware of things like IMD and harmonics, but experienced and knowledgeable people know and understand these things. You cannot "hear" harmonics in your signal as they are not even on the same frequency you are using. A dirty CB signal can wreak havoc on the 6m ham band, along with others. What you are saying is that it's your "personal preference" not to give a crap about who you interfere with. The rest of us don't like people like that, hence the responses you're getting currently.

The issue here is that every radio operator, regardless of service or amateurism, has a responsibility to keep their signal clean and trash free so that other operators don't have to deal with the garbage QRM caused by intermod and harmonic distortion. If an operator doesn't feel that this responsibility is important that's their decision, but other operators are well within their rights to label irresponsible operators as such.

There's the right way, and there's the wrong way. Not caring about the interference you cause is the wrong way to act as a radio operator. It's that simple.
 
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So basically what you're saying is that you've been to several forums acting like you have here and they've all banned you? Imagine that...

Here's the deal: Your mindset regarding 11m operation is garbage. This is not an opinion, it's scientific fact. You (and all operators) need to eventually learn what's really going on with transistor amplification and the signal byproducts produced when using transistors to amplify RF. It's never just as simple as "ooh boy, I've got moar powahhh!!!" There is always a price to be paid for more power, so most of the time it's about achieving good amounts of power while making sure that you're not putting out spurious garbage all the time, which interferes with other services and operators. Often some power must be sacrificed to maintain a quality signal.

There are too many operators (and not just on CB) that can't see past the end of their noses in terms of their operating technique. This selfish "I'm gonna do what I want, no matter how it impacts others" attitude is not good for anyone involved in radio. It bothers other ops (as I said earlier) and the bad ops catch grief (and rightfully so).

The thing that bothers me the most is that it's not ever very difficult to maintain a clean signal, and it's not even very hard to build DIY gear with signal purity in mind. The added circuitry and parts rarely amount to much in the way of cost or expertise to build, but the way so many hobbyists complain about the expectation of a clean signal you'd think that it was nuclear physics.
 
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there is a better mod posted here a while back by shockwave using a transformer bought at radio shack back in the day or you can use one from a 29 ltd classic or the one from a none working 148 the thread is under mosfet and 148 but for some reason the images of how is wired are gone if we can get them back it is an excelent mod for the 148 look here

http://www.worldwidedx.com/radio-radio-related-modifications/51465-mosfets-148gtl.html

start reading from post 11
 
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well imho i would just do the normal peak n tune up add a power mic and go
if i want more i add an amp kl-500 would fit the bill nicely with a
low drive radio like this .for big am swing get a cobra 29 with a rx75
 
1iwilly said:
there is a better mod posted here a while back by shockwave using a transformer bought at radio shack back in the day or you can use one from a 29 ltd classic or the one from a none working 148 the thread is under mosfet and 148 but for some reason the images of how is wired are gone if we can get them back it is an excelent mod for the 148 look here

http://www.worldwidedx.com/radio-radio-related-modifications/51465-mosfets-148gtl.html

start reading from post 11
Click to expand...

Good read, thanks.
 
eagle1911 said:
So basically what you're saying is that you've been to several forums acting like you have here and they've all banned you? Imagine that...

Here's the deal: Your mindset regarding 11m operation is garbage. This is not an opinion, it's scientific fact. You (and all operators) need to eventually learn what's really going on with transistor amplification and the signal byproducts produced when using transistors to amplify RF. It's never just as simple as "ooh boy, I've got moar powahhh!!!" There is always a price to be paid for more power, so most of the time it's about achieving good amounts of power while making sure that you're not putting out spurious garbage all the time, which interferes with other services and operators. Often some power must be sacrificed to maintain a quality signal.

There are too many operators (and not just on CB) that can't see past the end of their noses in terms of their operating technique. This selfish "I'm gonna do what I want, no matter how it impacts others" attitude is not good for anyone involved in radio. It bothers other ops (as I said earlier) and the bad ops catch grief (and rightfully so).

The thing that bothers me the most is that it's not ever very difficult to maintain a clean signal, and it's not even very hard to build DIY gear with signal purity in mind. The added circuitry and parts rarely amount to much in the way of cost or expertise to build, but the way so many hobbyists complain about the expectation of a clean signal you'd think that it was nuclear physics.
Click to expand...

See this is where you don't know as much as you think you do, the formentioned 148 does about 15w pep into a homebrew 1-1446x4-2879 that loafs along at a mere 650w pep, While I've seen it pushed to do around 1250w, I like to run it low to keep the temp down and the fact that 2879's are approaching $35 now... Even the hardest nosed old school operators around here comment on how clean it sounds. Now what does it look like on an analyzer, again I don't know, if I had one I'd tell you, but through the years of a lot of trial and error I've come up with what seems to work for me, nuclear physics played no part in it. Just because I enjoy the outlaw part of this hobby doesn't mean I can't run just as clean a station as the next guy.
 
it would be nice if anybody here that mess with the mod still have the photos laying around that they can re-post them??? i forgot the pin out of the transformer i now youwere suppose to use the primary side
 
137 said:
See this is where you don't know as much as you think you do, the formentioned 148 does about 15w pep into a homebrew 1-1446x4-2879 that loafs along at a mere 650w pep, While I've seen it pushed to do around 1250w, I like to run it low to keep the temp down and the fact that 2879's are approaching $35 now... Even the hardest nosed old school operators around here comment on how clean it sounds. Now what does it look like on an analyzer, again I don't know, if I had one I'd tell you, but through the years of a lot of trial and error I've come up with what seems to work for me, nuclear physics played no part in it. Just because I enjoy the outlaw part of this hobby doesn't mean I can't run just as clean a station as the next guy.
Click to expand...


Soooooo 4 X 2sc2979s making 650 watts is loafing along and sounds "clean"?
 
137 said:
Just because I enjoy the outlaw part of this hobby doesn't mean I can't run just as clean a station as the next guy.
Click to expand...

^See, now this is where you don't know as much as you think you do. All the "outlaw" in the world doesn't change the laws of physics, sorry.

I'm not saying this stuff just to blow off hot air. There's a lot more to this than you are understanding. I know this because you keep insisting that the "sound" of a signal is what determines if it's clean or not. In reality a "clean sounding" signal can have just as much (if not more) off-frequency trash in it as a "dirty sounding" signal. The trash that you really need to worry about is the stuff that you and the guy you're talking to can't hear, but your neighbors and other operators have to deal with.

I've already posted the facts here, and we all know you can lead a horse to water, but you can't make them drink.
 

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