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Questions & Upgrades - COBRA 148 GTL (TAIWAN)

Discussion in 'CB Radio Modifications' started by MC133, Jun 18, 2018.

  1. MC133

    MC133 New Member

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    Hello everybody have virgin Cobra 148 GTL (TAIWAN) mint in the box and I'm thinking of getting it
    professionally modded by Lescomm but before I make up a build sheet of what mods I want done
    I wanted to ask some opinions from some of you.

    Here's what I want so far.
    Lescomm channel expansion board 5200 with 3 digit display.
    Unlock clarifier 6 kc
    Full tune, peak & Alignment
    No audio limiters clipped
    Broadband Receive & Transmit
    Upgrade finals



    Now this I not sure about
    Schottky diodes for receiver ?
    High gain receive transistor ?

    I never had a 148 or any other radio with this mod.
    I not sure if I would like it.
    I always thought the 148's receiver was perfect the way it was, compared to most radios out their.

    What do you all think?
     

  2. Handy Andy

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

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    That radio is quite old, will need several things you didn't even mention.

    Consider them like time capsules - a lot like a car from that era - meaning they don't have spare parts for them at the body shop or at Auto Parts dealer - they may have a lot of memories behind them, and in getting it fixed, let alone the maintenance, it may set a price similar to the "Million Dollar Mile" you may wind up with a lemon.

    Did the radio have any storage issues? Look at the box, damp areas - mold, dry rot - may mean there is rust.

    Any of the above, it signals potential damages within.

    Any radio that isn't used from those times, 80's or 90's and stored in a box, may not work well after long term.

    The controls and switches, when they got put in the box - is what I'm talking about.

    The pressure and oxides - can prevent the switch from working right. You can't control whom may have opened the box and what they did with what's inside - to claim NOS or even OEM - only indicates you get the radio and all the accessories as listed in the owners manual. But you don't know if that radios been a "test subject" for a shop that let people come in a play with it's knobs and fiddle with the controls. Even hand prints and finger prints leave acids and can discolor the front panels' knobs and brushed aluminum panel. Let alone how long it sat out under lights as a display model - THEN thrown in the box after a quik dusting with Pledge and a Scott towel - lint and all.

    Some components, like Electrolytic capacitors, connectors - board rivets Control Bearings - all dry out from age - no matter what was done to preserve them - even the "rosin core" from back then can contain residual acids from the etchants used to make the board still left on the board

    Long term storage is not the best for composition and rheostats they tend to take pressure from the tension of the wiper arm making contact at whatever last setting they were at and dimple or "detent" - meaning they may no longer have a smooth rotation further meaning they may not rotate smoothly - they will hit a spot on the rotation and may cut out operation - requirement replacement. Some potentiometers have a carbon composition that can lift from the substrate it's applied to inside the part - breaking contact along the composition surface rendering it useless.

    These radios are gems, but they are costly to repair - they don't have OEM parts laying around in shops. So if you decide to use Lescomms - be prepared to pay for it.

    And that brings up another issue of how they will stand behind their work.

    I've had to rework other shops that said "Oh it worked fine on the bench" - only to see the radio on my bench with bits and pieces of foil wrapped around the audio chip, modulation transformer and see a capacitor "cratered" from the gassing caused by dried out plates that popped like a fuse from the dead short. That was before I powered it up - I pull the covers to review - have to - else you may be in for a nightmare you're stuck repairing.

    We haven't even talked about the speaker - OEM ones have a particular dimension - not too many places still make these types of designs for radios - so again, parts are not always off the shelf in radio shops.

    It's a labor of love more than a simple repair job - because the radio - the one you are getting - is a classic that many wish they still had because it was made during a time when Radio Audio was a quality issue - so they were designed with that in mind. You were in control.

    :+> Andy <+:
     
  3. sonoma

    sonoma Sr. Member

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    Les sent me a few emails this week that he had a sell for fathers day. he claimed to give a 20% discount on his radios and other items. one place I was reading on his site that mods are taking some time to do since he has a backup log of about 200 days. he stated in the article not to expect a fast turn around on some mods depending on what is wanted.. I took that to mean you could be waiting on the radio from 6 to 8 months. some he has for sale are ready to go since he has done some of the most wanted mods to his new radios.
    here is his email and shows to be good until 6/19/18 up until midnight.
    well the link will not go through as it should.
     
  4. sonoma

    sonoma Sr. Member

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    try this link

    http://store.lesterscustoms.com/

    here is what he stated in one location.

    Les's expertise is in high demand! At present the wait time is 8 to 12 months.

    I BELIEVE IN QUALITY BEFORE QUANTITY! (And from the sales I'm receiving, so do you!) SO IF YOU'RE IMPATIENT, DO NOT ORDER FROM ME!! Let me repeat that, IF YOU'RE IMPATIENT, DO NOT ORDER FROM ME!! I SIMPLY REFUSE TO RUSH MY BUILDS. Each radio goes through 24 hours minimum of burn-in testing when it's finished. IT WILL BE RIGHT WHEN IT LEAVES MY SHOP! Our Build Policy; Average turn around time for "CUSTOM BUILT RADIOS" is running between 180 to 220 days at present (May 2018).
     
    #4 sonoma, Jun 18, 2018
    Last edited: Jun 18, 2018
  5. sp5it

    sp5it Master of puppets

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    Do not butcher such a a nice radio.
    Mike
     
  6. wjm1129

    wjm1129 Member

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    I recommend leaving the covers on it and using it as is.
     
  7. Handy Andy

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

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    It is far better to keep the radio stock than to mod it, like you've shown you'd like to do with it.

    Schottky versus OEM?
    Schottky is a type of diode, has only 1 junction (usually N) versus PN types - so the voltage drop across it is less - which usually means less drop - more efficient. Votlage Drop ranges from 0.2 to 0.4 (max.)
    OEM - standard Silicon uses PN junctions and have a forward voltage drop of about 0.7V
    OEM - Standard Germanium uses PN junctions and have a forward Voltage Drop of about 0.3V.
    Similar to Schottky but were designed years - decades ago.

    It is a personal choice on Germanium versus Schottky - any radio can benefit from the upgrade - but is it worth the cost? In some cases - age before beauty - also accounts for the audio quality and performance - so a personal choice. You said it was mint condition - so I can only wonder why the need to upgrade when you haven't even used it in the first place? I can understand car tires but not glass sealed envelope diodes that HAVEN'T had much use - you did not tell us if this radio has even been powered up recently.

    Unlock Clarifier - Yes, by all means - done right though. 6kHz slide? Do the simple conversion of unlocking it first and use it that way for a while else only if needed to have done - a lot of this deals with current draw across parts like the Voice Lock control - that; as they age, can get tricky to operate due to bad spots and dirt in the chamber that houses the wiper arm and composition. So it may not work "linearly" and can jump - a good cleaning first and simply jumpering (relocate voltage source to a constant versus switched and breaking a switched line D56/D72 TX stuff) the Voice Lock Pot to the same Voltage power feed the PLL and don't change any resistor if you can, it's is not necessary and if done like I said, the drift is less and you have more than enough slide for most QSO's (conversations).

    Receiver upgrade? Look thru this thread...
    https://www.worldwidedx.com/threads/how-to-perform-the-2sc2999-and-schottky-diode-swap.23680/

    The thread is long but look thru it to see if it's something you want...
    Because below is a partial schematic of what you have in the radio - and so review their conversion procedures listed in that thread before you have this done. It's marginal improvements - and Schottky would take on most of the issues and give you potentially a better, quieter receive than to upgrade the RF amp and front end.

    Cobra148GTLFrontEnd.jpg

    Now, you may not care to understand the above, but you are asking for opinions. Because if you don't know what is IN the radio - they can do some simple stuff and SOAK YOU for their falsehood.

    It would be a wise idea to protect yourself and take photos - camera or phone (use MACRO setting for Focus) and open that radio case and take pics, for that may be your only defense against fraud.

    Because, a lot of that radio uses parts that are not on store shelves and commonly found - it's more extinct than proprietary these days.

    The PIN front end protection is one area that has a particular type of performance curve that makes this radio what it is. The RF amp? Many would say just keep it - others would say try the 2SC2999 - READ THE LINK ABOVE for that... then decide SCHOTTKY is included in the thread - I recommend you read it.

    :+> Andy <+:
     
    #7 Handy Andy, Jun 18, 2018
    Last edited: Jun 18, 2018
  8. nomadradio

    nomadradio Analog Retentive

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    The very last 148 made in Taiwan was in 1989 IIRC.

    You may imagine that if you have a mint, low-mileage 1989 car that bolting on all the latest mods may not get you all the high-performance results you hoped for.

    30 years is 30 years. Not quite long enough to recommend replacing ALL the aluminum electrolytic caps, but there are a few of them that tend to fail first in that radio. Might get a year from it before some of those parts remember how old they are and begin to fail.

    Might get a week.

    The good news is that several of the most-common faults can be blamed on well-known specific parts.

    You should listen to Andy about the receiver mods. This radio is sought after by some folks precisely because it's fairly quiet. Compared to most post-Y2K radios at least. All the mods you mention either do nothing, or raise the receiver's internal-noise level.

    The one thing I suggest watching out for is "dead flush" tuning slugs on the small "can" IF and RF trasformers/tuning coils. If it was exposed to high humidity, you may find that when the radio is aligned, one or more of the small slugs with the tiny slot on the end will appear to peak at this "dead flush with the rim" position.

    If you see that, this adjustment is not really peaked. Just appears to be. The dead-flush position of the small slugs is where the control is at its max setting. Any tuning adjustment that gets "peaked" for max signal should adjust somewhere in between the max and min limits. That dead-flush-with-the-rim-of-the-hole peak tells you that circuit has a defect, and it's not really a true peak setting you're seeing.

    73
     
  9. MC133

    MC133 New Member

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    Thanks for all the advice and your time.
    I know it's an old radio but i like it for it's nostalgia.
    I will take your advise and test it out and make sure everything works on the radio and check out how it looks inside before going forward with anything.
    This is just something I was thinking of doing and there's no
    rush on it.
    I just thought it would be cool to get this thing up and running.
    If I do end up going forward with all this what do you all think of my list of mods? Any do's & don'ts?
     
  10. Low_Boy

    Low_Boy Active Member

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    Buy a Cobra 148 GTL that is not so nice. Buy a face plate, bezel covers and have that one modded. Keep or sell the new old stock radio. Don't butcher it.
     
  11. dave457

    dave457 Well-Known Member

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    Recap and factory alignment
     
    Dmans likes this.
  12. Handy Andy

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

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    See above...and remember there is a lot of respect for that radio.

    This List is Incomplete And Will Be Supplemented As Necessary.

    :+> Andy <+:
     
  13. Mustang 131

    Mustang 131 Well-Known Member

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    Leave it stock. Plenty of hack radios to be found. Just buy a radio that that crap in it.
     
  14. MC133

    MC133 New Member

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    Thanks for the advice. The main reason why I wanted to get it modded so I could work some SSB DX above 40ch.
     
  15. MC133

    MC133 New Member

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    I remember getting my first Cobra 148 in 1993 it was a 91 Philippines radio I was only 15 years old I and it cost me $170.
     

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