Cobra 142 GTL Mic wiring?

[loosecannon]

yes, that pot on the power supply board will adjust the DC voltage that goes to the main PC board.

the transistor i was referring to is not your final amplifier transistor, it is the AM power regulator. just want to clarify.

upgrading the driver and final in these radios is not worth it.
they already have about the best gain you are going to find.

yes, your radio probably has the AMC disabled somehow, and who knows what other mods.
a radio that deadkeys 2 watts and swings to 12, and a squealing D104 are good signs that the limiter has been clipped.
LC

 

[Simbalage22]

TR32 in the front right section of the board is the one people usually clip, even though it makes the radio sound like crap on AM and SSB.
replace it with a 2SC945 or equivalent.

also check to see if R104 has been clipped. this one only affects the AM audio, but if you want the AMC intact, this resistor needs to be there.

VR6 will set your deadkey.
VR7 will set the SSB power. (do not go over about 15 watts)

L36 and L37 near the driver and final are your TX peaking adjustments.
make sure you tune them for max "modulated" power while saying "ahhh" into the mic.
do not tune them for max deadkey or you will end up with downward modulation.
LC

Finally got around to opening it up.. TR32 is intact.. cant find R104, And the chip your referring to is indeed a 1419.. So would I be ale to take that one you are referring to out of another electronic device, or should I go new? If they didnt clip how is this doing 2dead-12 swing? Going to check the power now but wow! Like that they didnt overmodulate this thing

 

[loosecannon]

R104 is a 10k resistor that is connected to the Base of TR33.

should be just to the rear of where you found TR32.

it might not be labeled, and it might be soldered into a spot marked for a diode.
it happens because this same board is used in different radios with different features.

my guess is that it has been cut or removed all together.

there is another hack mod that people like to do to this chassis which involves lowering the value of two resistors in the mic audio line that is supposed to make the radio louder.
what it really does is make the mic more sensitive and prone to squealing.
they are R99 and R94, and should be found in the same general area as TR32 and TR33.
they should both be 10k resistors, but people change them out to 4.7k or even 2.2k in an attempt to squeeze every bit of audio they can out of the radio.
its actually counterproductive because you have to turn the mic gain down so the radio wont squeal. LOL

speaking of mic squeal, there is an electrolytic cap whose value can be increased to help prevent the mic from squealing.
it is C92 and the stock value is 47uF. i up its value to 1000uF, but 470uF should be just fine.
it all depends on what you can find that will fit, as its a crowded area.

as for the 1419 regulator, you could probably look up its datasheet and find a sub, but the NTE152 should be pretty easy to find and be pretty cheap.
there is another 1419 on the power supply board, its TR302 and i like to replace this one also. i usually attach it to the power supply heatsink and run wires to the board, but thats just me.

i also like to up the value of the main filter caps, just to give the radio more breathing room.
C304 on the power supply board is a 3300uF 35v cap and i like to use at least 4700 if not 6800, depending on what i can find.
do not use a 16 volt cap as this cap sees about 18 volts from the bridge rectifier.
i always use either a 35v or a 50v part, whichever is available.
i also upgrade C134, the filter cap on the main PC board to a 2200 or 3300uF 25v cap.

these cap changes are just things i do because im that way, but i do believe that it benefits the overall operation of the radio.
to what extent is debatable.

oh yeah, one more place to look for a modulation mod is just to the left of where the AM reg (1419) is mounted.
find R228 and see if someone has put a small silicon rectifier diode in series with it.
this is sometimes called a "swing mod" as it allows the radio to get full swing from a reduced carrier.

well, thats it for now, im sure there is more that im forgetting,
LC

 

[Simbalage22]

R104 is a 10k resistor that is connected to the Base of TR33.

should be just to the rear of where you found TR32.

it might not be labeled, and it might be soldered into a spot marked for a diode.
it happens because this same board is used in different radios with different features.

my guess is that it has been cut or removed all together.

there is another hack mod that people like to do to this chassis which involves lowering the value of two resistors in the mic audio line that is supposed to make the radio louder.
what it really does is make the mic more sensitive and prone to squealing.
they are R99 and R94, and should be found in the same general area as TR32 and TR33.
they should both be 10k resistors, but people change them out to 4.7k or even 2.2k in an attempt to squeeze every bit of audio they can out of the radio.
its actually counterproductive because you have to turn the mic gain down so the radio wont squeal. LOL

speaking of mic squeal, there is an electrolytic cap whose value can be increased to help prevent the mic from squealing.
it is C92 and the stock value is 47uF. i up its value to 1000uF, but 470uF should be just fine.
it all depends on what you can find that will fit, as its a crowded area.

as for the 1419 regulator, you could probably look up its datasheet and find a sub, but the NTE152 should be pretty easy to find and be pretty cheap.
there is another 1419 on the power supply board, its TR302 and i like to replace this one also. i usually attach it to the power supply heatsink and run wires to the board, but thats just me.

i also like to up the value of the main filter caps, just to give the radio more breathing room.
C304 on the power supply board is a 3300uF 35v cap and i like to use at least 4700 if not 6800, depending on what i can find.
do not use a 16 volt cap as this cap sees about 18 volts from the bridge rectifier.
i always use either a 35v or a 50v part, whichever is available.
i also upgrade C134, the filter cap on the main PC board to a 2200 or 3300uF 25v cap.

these cap changes are just things i do because im that way, but i do believe that it benefits the overall operation of the radio.
to what extent is debatable.

oh yeah, one more place to look for a modulation mod is just to the left of where the AM reg (1419) is mounted.
find R228 and see if someone has put a small silicon rectifier diode in series with it.
this is sometimes called a "swing mod" as it allows the radio to get full swing from a reduced carrier.

well, thats it for now, im sure there is more that im forgetting,
LC

Cool, I will definatly check this out. Yea I'd like to get the most of out the radio without overdriving it. So far (with dyna turned down w/ d104 mic) it sounds good and its reaching out really far, With a 2w deadkey its amazing. But I will check those that are posted above and post results.. I am wondering how they tuned it without the epoxy being touched on the pots.. Weird but I am definatly going to replace the 1419 if thats a good move because I like this radio and plan on keeping it anyways..



UPDATE: R104 is intact, TR32 looks like a diode unlike the others marked "TR" are black...
R99 & R94 are both in range.. cant find R228 would that be a good mod? I am going to update the caps, and both 1419 chips, but do I have to upgrade them before I upgrade the caps as you mention? Being you have experience with these, I want to get the most out of this old radio without overdoing it and burning it up.. Also is a lower deadkey better or should I raise it? Also with a linear should it be high or low. I have a high drive.. But generally speaking whats good dead key without linear, and with one? and whats the best this radio can confortable put out when done modding? Deadkey-Swing?

Thanks a million.. You have helped not only get the mic right, But I am learning this radio quite well thanx to you Modding is funner then talking .) I had fun modding my Cobra With weather.. My uncle said it was impossible to get 40W I did some mods and changed the finals and he was amazed what that little thing did. I gave it to him.. He is old and really into the hobbie..

 

[Simbalage22]

PixOfMyRig

Here, Not sure they are helpful. Full scaled (Not Resized) Of the Radio Inside

 

[loosecannon]

the pics give me a reference to go by to show you where things are, so they are helpful.
i cant quite tell, but it looks like TR32 may be gone.

using your second pic as a reference; look at C92, and just to the right of that there is a green mylar cap. just to the right of that cap it looks as though there is a space where a transistor used to be.

can you describe in detail what you see in the actual radio?
also look at the bottom (green side) of the PC board right where that transistor marking is. is there anything soldered to the board from the bottom there?
TR32 can be hard to determine from the other transistors near it.

it also looks at though L36 (the brown plastic coil with the big ferrite slug in it near the final transistor((2SC1969)) has not been touched.
this is not a big deal as it really wont gain you much power if you do peak it.
the possible issue im seeing is that it looks like L39 (looks the same as L36 but is near the antenna connector) might have been turned by someone who thought it was the right one to peak.
L39 is your TVI trap and is meant to keep harmonics out of your signal.
if this is turned, it can cause a "splattery" signal, TV interference, and might even cause your wattmeter to give a false reading.
the way i learned to adjust it if it had been messed with earlier was to tune a TV set to channel 2, key the radio and adjust it for minimum interference.
not sure this would work with newer TVs as they dont show the "snow".
the correct way to adjust it is with a spectrum analyzer, but they are VERY expensive.
tell me what you see in the actual radio.

now for your questions.

the R228 mod is really not needed IMO.
these radios are some of the best sounding radios ever made and just need a good alignment to sound great.
doing mods like this can also cause splatter in your signal.

as for replacing the caps and the 1419's, it doesnt matter which you do first, or when.

to answer the rest of your questions about deadkey and linears, i need to know what type of linear you are going to run.
what brand?
how many transistors are in it? (these get referred to as "pills" a lot because they kind of look like big asprin)

most likely, the deadkey was lowered in your radio by adjusting VR6 precisely because the old owner was running an amp with it.
most amps like less than a 4 watt deadkey input. (but it depends on the amp)

this radio should be set to no more than a 5 watt deadkey and should swing to about 18-20 watts PEP.
the SSB should be set to no more than about 15 watts.

here is the big untold truth about trying to squeeze more power out of a radio. many will disagree with you on the CB band about this, but it IS the truth.

to increase your signal by 1 S-unit in someone's receive, you have to quadruple your power output.
lets say you are deadkeying 5 watts and hitting someone with an S-3.
to get to S-4 you will have to deadkey 20 watts.
if you are deadkeying 500 watts and hitting someone with an S-3, you will have to deadkey 2,000 watts to get to S-4.
thats just the way it works and it shows you why its not really worth it to try and mod a radio to death.
no one will notice the difference, except your modulation might suffer from the mods.
you can easily see why a 2 pill linear is the best bang for your buck as far as signal gain goes.
LC

 

[Simbalage22]

Ok cool.. Yea I am currently running a 2 pill (Texas Star 250 HDV) So its a high drive,, Thats why I asked because I was told regular linears are supposed to have 2W dead key.. Wasnt sure about high drive... And also wasnt sure if turning up the deadkey would make it better. I will check that later on tonight or tommorrow and respond back with the information. TR32 if its a diode looking 2 leg then its still there. As far as memory serves the one next to tr32 is there but looks like a diode.. but the rest of the items marked with TR are black and have 3 legs.. Will post more info later tonight

the pics give me a reference to go by to show you where things are, so they are helpful.
i cant quite tell, but it looks like TR32 may be gone.

using your second pic as a reference; look at C92, and just to the right of that there is a green mylar cap. just to the right of that cap it looks as though there is a space where a transistor used to be.

can you describe in detail what you see in the actual radio?
also look at the bottom (green side) of the PC board right where that transistor marking is. is there anything soldered to the board from the bottom there?
TR32 can be hard to determine from the other transistors near it.

it also looks at though L36 (the brown plastic coil with the big ferrite slug in it near the final transistor((2SC1969)) has not been touched.
this is not a big deal as it really wont gain you much power if you do peak it.
the possible issue im seeing is that it looks like L39 (looks the same as L36 but is near the antenna connector) might have been turned by someone who thought it was the right one to peak.
L39 is your TVI trap and is meant to keep harmonics out of your signal.
if this is turned, it can cause a "splattery" signal, TV interference, and might even cause your wattmeter to give a false reading.
the way i learned to adjust it if it had been messed with earlier was to tune a TV set to channel 2, key the radio and adjust it for minimum interference.
not sure this would work with newer TVs as they dont show the "snow".
the correct way to adjust it is with a spectrum analyzer, but they are VERY expensive.
tell me what you see in the actual radio.

now for your questions.

the R228 mod is really not needed IMO.
these radios are some of the best sounding radios ever made and just need a good alignment to sound great.
doing mods like this can also cause splatter in your signal.

as for replacing the caps and the 1419's, it doesnt matter which you do first, or when.

to answer the rest of your questions about deadkey and linears, i need to know what type of linear you are going to run.
what brand?
how many transistors are in it? (these get referred to as "pills" a lot because they kind of look like big asprin)

most likely, the deadkey was lowered in your radio by adjusting VR6 precisely because the old owner was running an amp with it.
most amps like less than a 4 watt deadkey input. (but it depends on the amp)

this radio should be set to no more than a 5 watt deadkey and should swing to about 18-20 watts PEP.
the SSB should be set to no more than about 15 watts.

here is the big untold truth about trying to squeeze more power out of a radio. many will disagree with you on the CB band about this, but it IS the truth.

to increase your signal by 1 S-unit in someone's receive, you have to quadruple your power output.
lets say you are deadkeying 5 watts and hitting someone with an S-3.
to get to S-4 you will have to deadkey 20 watts.
if you are deadkeying 500 watts and hitting someone with an S-3, you will have to deadkey 2,000 watts to get to S-4.
thats just the way it works and it shows you why its not really worth it to try and mod a radio to death.
no one will notice the difference, except your modulation might suffer from the mods.
you can easily see why a 2 pill linear is the best bang for your buck as far as signal gain goes.
LC

 

[loosecannon]

those parts are so close together that it can be hard to tell which part the label is referring to.
TR32 is indeed a black TO-92 transistor with three legs.
if it has been replaced by a diode, it is effectively removed from the circuit and should be replaced with a 2SC945 or equivalent transistor.

as for the amp, even though it is a high drive amp, i wouldnt deadkey more than 3 watts into it.

the best way i know to set the deadkey for an amp is to look at your wattmeter while saying "ahhh" with the amp on full power, and make a note of the reading. lets say its 200 watts PEP.
now deadkey the amp and adjust the AM POWER control (VR6 in your radio) so that the deadkey out of the amp is 1/4 of the full PEP output.
in our example that would be a 50 watt deadkey out of the amp.

im gonna bet that the radio ends up deadkeying between 2 and 4 watts after this.

is your amp variable?
while im not too familiar with the variable texas star amps, but i have heard that the variable pots can burn out over time.
i think you can just jump them out of the circuit and leave the power up all the time, but dont quote me on that.

we happen to be fortunate enough to have a member here in this forum that used to work for Texas Star repairing amps, and you can email him for advice on your particular amp. his screen name is texasstarrepair and you can find his info here:http://www.worldwidedx.com/amplifiers/59097-texas-star-amp-repair-free-help.html

i would be interested in what he tells you for my own knowledge.
LC