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Cobra 25 NW ST WX Questions, tips. A multipurpose, multiquestion thread.

Discussion in 'CB Radio Modifications' started by Cutlass327, Oct 1, 2018.

  1. Cutlass327

    Cutlass327 Member

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    Somehow I posted this in the wrong section... twice I've done that?? Copy pasted and deleted from other location:

    OK. I now have 2 of these radios, one bought new (MFR FEB 13) and an eBay special (MFR July 04).

    Both have had the Cobra TSB for diabling the Soundtracker done.

    My setup, a Radioshack 4' mag mount (about the equivalent to a Wilson Lil Wil) on my filing cabinet, SWR 2.0:1. Temporary test load until my MFS 300W dummy comes in Tues (Oct2). Computer 13.8V 30A Power supply. Main antenna I am working on putting up is a Solarcon A99 on a 30' pole, 100' rg8x coax.
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    1. The '13 radio I have added a RCI EB-2015 echo to, the 2nd one I want to but have a question on doing it. I would like to remove the Dim/Dyna knob and put the echo there. What does it take to eliminate the knob for the Dyna side? I plan to set the dimmer, measure the resistance, and just install a fixed value resistor there in place of the VR. Looks like there are 3 wires to each part of that control set...
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    2. OK. Another thing. I opened the 04 radio, D9 was clipped, (I think it is L10) was turned out fully, the ceramic cap from the 8 or 9 pin chip on the side wall of chassis to chassis was clipped. I cannot see any other obvious changes. I put it on my Dosy TC, modulation swung high, dead key about 6W, but here is my observations...

    Modulation pegs meter, but then drops to about 75% without changing my "auuuudio".
    Deadkey 6, but only swings to maybe 7 or 8.

    I turned L10(?) slug in, dk dropped, but still no matter how I adjusted it it only went maybe 2w swing.
    No wire coils spread, all are tight and still glued (thankfully! No harmonics measured.)

    Soldered D9 back together. Adjusted VR5 to the "Set" lone on the meter for a solid reference point. Still drops with voice. Read somewhere about finding a 1kHz audio online, played it thru the mic. Modulation held steady. Maybe my voice gets weak after a moment...

    Resoldered ceramic disk cap to chassis. No difference. Thinking it is a filtering cap??

    Is the 2W swing normal, and is that sufficient to sound strong and clear? I always see 1:4 ratio, I am nowhere near that.
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    I am planning to use this thread for any questions I may come up with with these 2 radios. I have searched a lot, only found a few things on the modulation, and they were mostly add a "swing kit" cap and resistor. I kind made notes of what and where I found some info:

    Copper:


    Modulation: VR5 or Cut D9

    AM Power: L10, L9, L8

    Notes: VR1 Squelch Adjustment VR3 Transmit Meter VR4 Squelch VR5 Modulation Meter VC10 = 10.240 Xtal Adjustment POWER MOD! #1 - Change R76 (3,3K) to a 1K (located near Mic Socket} #2 - Change R43 (10 Ohm to a 2.7 Ohm #3 - Change R108 (1Ohm to a .47 Ohm #4 - Re-Tune L10, L9, L8 for MAX Forward Power

    WorldWideDX.com:
    (Thread about more audio)
    Loosecannon: you can also try changing C91 to a 33uF electrolytic cap.
    this affects the AMC attack time.

    CBTRICKS.COM:

    Secret CB:

    1. R76 (3.3K), Change to 1K

    2. R53 (47K), Change to 22K

    3. C89 (.033mfd) change to 2.2mfd (Note: makes sure + side is not next to IC)

    4. If more drive is needed the final may be changed to 2SC1307 or ECG-236

    CBRADIOTALK.COM:

    Pokeyman:



    install 2SC1969 power transistor. Exchange D10 with Schottky diode.
    Exchange R43 (at driver) with a 1.5-2.2 ohm 1/4 watt resistor. (Stock unit is an 8.2-10 ohm)
    Exchange R40 (at final) with a 8.2-10 ohm 1/4 watt resistor. (Stock unit is a 22 ohm)
    Optimize output for each radio by bridging a 33, 47, or 68pf at C46 and C42
     

  2. 9C1Driver

    9C1Driver Sr. Member

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    The soundtracker Cobra's were probably the worst of the brand they ever had made for them. (Cobra has never actually made a radio of their own) This is how they got the nickname of "Soundcrapper". That said if your radio's are both working I would just run them. At the most give them a light tune and alignment. There your done.

    If your wanting to just mess with some mods and learn how to do things then those are perfect for that. If you burn them up or they get so messed up they don't work it's no great loss. Have fun learning some mods. Remember though some mods work ok, many don't accomplish much at all really.
     
    Cutlass327 likes this.
  3. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    It would be in your best interests to get back to CB Tricks and locate the schematics for the Cobra 25 - and all its' variants LTD, GTL - ST - WX - NW - NWSTWX and of course the infamous SUX variant.

    Might have to dig for it but you can start by clicking on their "Radio Information" link on the left side of your screen.
     
    #3 Handy Andy, Oct 3, 2018
    Last edited: Oct 3, 2018
  4. Robb

    Robb Yup

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    IIRC - there is a page on CBTricks that shows how to disable the ST function in that radio. Only requires lifting a couple of SMD's. Other than that, I really wouldn't try to milk every last watt out of the radio by using so many mods to the stock chassis. Usually, the cap/resistor mod swing kit works remarkably well so long as the radio gets properly re-peaked after that mod.

    Seems that so many get hung up on getting every little bit of power regardless if the radio ends up sounding like crap. There is a fine balance between a loud radio and on that is sufficiently louder yet remains clean transmitting. Like I said - a fine balance needs to be achieved to call it a success
    JMHO . . .
     
  5. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I am curious though, what is it you want out of this thread for those radios?
     
  6. Cutlass327

    Cutlass327 Member

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    I have already disabled the ST, that was one of the first things I did.

    My main thing is to get them as best sounding as I can with minimal stuff, and on the older one kinda play around and see what I can do. Being it is already tampered with inside, of unknown modification, I was trying tto get a baseline as to how bad they screwed it up. This is the basis on the power swing question. It seems to transmit, and modulation is up there, I am just curious if I am missing something. I am too rusty on the insides of these to remember how things affect others.
     
  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    One of the many numerous problems with ST units were - not everyone uses ST. So the problems were from the Audio the radio had to work with. Compression side had squeals and Expansion side had noise level and audio envelope tracking problems. The ones with audio expansion were the most ridiculous - audio COMPRESSION was ok, the expansion part of it and a guy with a ton of echo on a wildly swinging carrier - well - it's best to describe it as - the guy sounds like the idiot he is, only with fade for emphasis. WhaT WHatTTT HHh-hh-EEE-eee-YYY! I cannot develop any way of showing it via text - it's something you'd just have to hear or leave to imagination.

    So if you've removed the 4066 chip - you also reworked and reconnected the audio receive and transmit lines in the radio to standard platform...

    So as you review the schematics of the various radios -same platform- just the variants (refer:SUX) - they did use different values as to affect the radios ability to provide envelope "swing" to power. They also added in some extra support parts (loose term) for providing a better sounding receiver.

    So the main crux of this is, you have to undo the changes they did to the platform, and re-do them with the parts and configuration to produce what you want - you have to put all that in.

    Audio Amp section and Limiter action were also affected - so even the output cap to the Reactance Modulator (Transformer) and the output filtering of that line to the Driver and Final - were "tweaked" as well.

    So look at the Final and Driver parings, their coupling techniques, as well as biasing scheme - for starters. You'll find they did change some caps to the output network to affect the level of filtering and admittance they worked with. So you may get thrown for a loop over some of the design re-work. All of it is for the "tightening" of the envelope swing and the amount of audio BANDWIDTH they used to compress all the audio into a tighter envelope.
     
  8. Cutlass327

    Cutlass327 Member

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    I think my biggest issue is there are no CB shops around here . I have heard of one about 45min from me, but I have heard mixed reviews on how they do things. The next closest is probably hour and a half away. I'm seriously considering sending out my 2 Galaxies to DTB In Carlisle for a good going over. I just hate the idea of shipping things...
     
  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Hmmm...OK...

    Well I do understand that if there isn't a local supply of parts, you're pretty much left to the whims and whimsicals of the local CB Shops. Even if they are miles away.

    Which what makes you even more vulnerable to fraud and being ripped off - kinda the same thing but one is a major event while the other is a nickel and dime type. Both are bad, and can ruin the learning experience you're trying to have out here.

    The problem lies in buying the particular parts that gave one platform the performance changes you want to see in another - it's not that easy...
     
    Cutlass327 likes this.
  10. sonoma

    sonoma Sr. Member

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