I just got this for $10.00. Works and looks good but only does around 11 watts and it will not hit 100% modulation even with a power mike. I have looked around and can not find any info on this. Can someone help me out?
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Tune up tips for a Cobra 29 23 channel.
- Thread starter King Mudduck
- Start date
They really don't do alot , but they will work well and sound very good , have heard many with D-104s on them sounded very nice indeed. 
L7 and L8 should be power and D-24 should be the limiter ? if not , you can just solder it back together. You can pretty much do what you want , I honestly didn't see it go to much over 100% with a clip . but you can also add resistor to diode if it means that much to you. Iv'e seen about 15 watts or so from them radios , I think in some cases they are better set to run amps , if you drop the power to run a amplifier , chances are the audio will grow closer to the 100% mark your looking for without a clip . Have fun.
L7 and L8 should be power and D-24 should be the limiter ? if not , you can just solder it back together. You can pretty much do what you want , I honestly didn't see it go to much over 100% with a clip . but you can also add resistor to diode if it means that much to you. Iv'e seen about 15 watts or so from them radios , I think in some cases they are better set to run amps , if you drop the power to run a amplifier , chances are the audio will grow closer to the 100% mark your looking for without a clip . Have fun.Here are some untested ideas that I can suggest after looking over the SAMS schematic for the 29 (23ch). Change C69 from a 10uf to about a 100-220uf. This should allow more energy from the audio amp to get to the final/driver. Short R97 to allow more audio form the mic to reach the mic preamp. The SAMS manual doesn't show any AMC circuit, but if I remember correctly the radio does have one. I do not recall if it has a limit adjustment, though. The CB Tune-up Manual, Volume 1, says to clip one end of D24 for modulation, but there is no D24 in the SAMS schematic. If you can locate D24, I'd insert a resistor to bring up the level. Experiment with values to get the right level.
On a side note, those so-called Tune-Up Manuals are ok for general referrence as far as actual tune-ups, but you would be wise to ignore anything they say about cutting or removing modulation limiter parts.
On a side note, those so-called Tune-Up Manuals are ok for general referrence as far as actual tune-ups, but you would be wise to ignore anything they say about cutting or removing modulation limiter parts.
but you would be wise to ignore anything they say about cutting or removing modulation limiter parts.
to many radios I've been through or owned myself over the years , there wasn't a whole lot more you could do to them , when it comes to limiters ,sure you can add or change resistor values if it really seems to be that bad by someone else ear hole ,(Unless you have a shop full of goodies and parts that one would need to do more) especially ones with mic gains that don't have VRs' in them , or ones that don't have either going for them, other then that , I think it can be somewhat ticky tack and I personally don't think anything has to be perfect. This is a hobby for some and folks like to try different things , especially with 10 dollar yard sale specials. Yeap , for some tech's , certain radios are a blink of an eye to tune up , and 30 to 40 dollars in the ole pocket 5 minutes later (-: 3 to 4 turns and your done , well sure , it could be a few more. Don't mind me much DTB , IM just having fun and that's what it's all about for me, and I love those books you spoke of , but even with the books , without the proper equipment or the know how to use them , it would be fairly tough on anybody to be as perfect as one could possible be..................OH Yeah !! You ought to squeeze in where Justin left off and get yourself a tech section like he had in the Forum , couldn't hurt and IM sure it would be great for some extra business for you . Happy Holidays to you.
to many radios I've been through or owned myself over the years , there wasn't a whole lot more you could do to them , when it comes to limiters ,sure you can add or change resistor values if it really seems to be that bad by someone else ear hole ,(Unless you have a shop full of goodies and parts that one would need to do more) especially ones with mic gains that don't have VRs' in them , or ones that don't have either going for them, other then that , I think it can be somewhat ticky tack and I personally don't think anything has to be perfect. This is a hobby for some and folks like to try different things , especially with 10 dollar yard sale specials. Yeap , for some tech's , certain radios are a blink of an eye to tune up , and 30 to 40 dollars in the ole pocket 5 minutes later (-: 3 to 4 turns and your done , well sure , it could be a few more. Don't mind me much DTB , IM just having fun and that's what it's all about for me, and I love those books you spoke of , but even with the books , without the proper equipment or the know how to use them , it would be fairly tough on anybody to be as perfect as one could possible be..................OH Yeah !! You ought to squeeze in where Justin left off and get yourself a tech section like he had in the Forum , couldn't hurt and IM sure it would be great for some extra business for you . Happy Holidays to you.
Thanks guys. I use a D104 on it and everyone who hears it thinks im full of BS when i tell them what it is. I went down the road and had my wife talk on it so i could hear it and it really does sound good!
first one I used for 4 years as a base was a Cobra 85 dynascan , I could plug in extra crystals into the exstention speaker jack for extra channels , it did about 5 to 15 watts , and the limiter or transistor had been removed. D-104 only needed to be cracked open , the radio did well and sounded very nice off a old Wilson 5/8 wave (Now what is called a Alpha V-5/8 by Maco) , I talked all over the world on that radio with only the power of the radio , Great DX and extra channels at that time surely helped my cause. I just went through a 29 like yours a few months back . it was remarkabley close to mint and had never been touched , there was no need to clip anything other then to bring the power down for his amp , pretty much had brought the audio up enough for it to sound very nice with that full audio sound. I truly have a passion for older radios , not so much crystal controled but right around 1976 and on .
I ordered 2 of these cobra 29A radios from ebay dirt cheap and hopefully atleast one of them work because they look almost new in the pictures but oh well we see what gets here.
I collect 23 channels and that's all I talk on
I collect 23 channels and that's all I talk on
The 23-channel Cobra 29 was type accepted before the FCC required a modulation limiter. Cobra (Uniden) was required to add this, er, "feature" to the original design. The schematic in the Sams book for this model shows it drawn in dotted lines. They did it by feeding a positive control voltage to the emitter of the mike amplifier transistor. Not the slickest way, but made the radio legal for 1974. Pretty sure that's the year this happened.
Newer radios use better methods to control mike gain and hold the modulation below the limit. By the time 40-channel versions of this radio came around Uniden fixed their mistake and later "29" models just sounded better.
73
Newer radios use better methods to control mike gain and hold the modulation below the limit. By the time 40-channel versions of this radio came around Uniden fixed their mistake and later "29" models just sounded better.
73
I took a chance and performed these very mods to my cobra 29A 23 channel and they worked flawlessly while not making any other components work harder and now my radio has all the audio I'll ever need that's well over 100% with a stock hand mic.
Can you look at your sams book and tell me which transistors are the driver and final outputs for the transmitter section please ?