Finally! A practical use for the Cobra 148GTL-DEE

[nomadradio]

At last! A practical use for the Cobra 148 Gee Tee Ell "DEE" radio. Cobra shopped around for low bidders to build the 148 for 25 years and finally succeeded in ruining it. The "D" apparently stands for "Dog".

It's famously useless for sideband. Never mind why. At least it can serve as an organ donor to keep an older 148 alive. Just one problem. The "LA" prefix type numbers used by Uniden for the 10mm slug-tuned coils and IF transformers got replaced by a simple 3-digit number. Here is a preliminary cross reference from the old radio's LA type to the new 3-digit type numbers.

But here's how it looks with the front panel and controls unhooked. Just the naked pc board.

The solder side.

It's probably best to remove the two metal shields first.

So here it is, the marriage made in heaven. Our parts-donor board and a propane torch.

A light touch is easy to say, but just do it outside and stand upwind.

The technique, if you can call it that, is to play the flame over an area of the board and slap the chassis down onto a table surface you don't care about.

Outdoors.

Here are the main targets for recovery. These 10mm RF/IF coils are essentially obsolete and more trouble to track down as time goes by.

Only one of them suffered a missing pin. Probably got it a bit too hot.

The scorching penetrated to the component side, but you can see what comes loose. Stuff you want and lots of disc caps, resistors, diodes and transistors you may or may not want.

So here is the haul. 24 10mm coils. Should be 25 but one of them had already been "harvested" before this process. A MMB8719, the balanced modulator chip, two crystal filters, a ceramic filter four quartz crystals, VCO module and a whine choke. You'll need to pry the tabs on the choke and SSB filter upwards to get them loose.

Cobra 148GTL-D with KEPC-332-G2 pcb uses the same tuneable inductors as the older versions, but with new numbers. This will cross the new part numbers to the older Toko "LA" numbers.

L21 is missing because it was already gone.


Schemo Toko# KEPC#
callout

L1 LA038 179
L2 LA179 180
L3 LA163 204
L4 LA261 200
L5 LA260 135
L6 LA259 188
L7 LA258 182
L8 LA257 199
L9 LA268 201
L10 LA269 183
L12 LA270 190
L13 LA272 203
L14 LA271 197
L15 LA264 202



L19 LA216 193
L20 LA195 186
L21 LA256
L22 LA051 185
L23 LA285 191
L30 LA266 196
L31 LA265 199

L45 LA254 187
L46 LA220 181
L47 LA160 192
L48 LA219 198

L59 LA284 184


With any luck I'll stumble across another 148"D" cadaver and proofread this list for accuracy.

73

 

[BayouRadioAmplifier]

hey! hold on, hold on, before you destroy another.....

I was "very quickly" given a nice looking but not working "D" radio
about 2 years ago, after asking a local about getting a CB with SSB mode.


.

.
first problem - no TX modulation, and also receive audio
was scratchy. found that newer big fat ugly Cobra microphone
had a bad element, and the switch contact for receive speaker
audio to be bad. so wired up this older Cobra microphone.

then found the usual MOD, the RF GAIN was modified to adjust
the RF output carrier level. I wired it back to stock, so now I can
lower the receive RF gain to listen to these guys around me having
300 watts and more of over modulated signals.

then what I wanted this radio for, SSB, did not sound very good.
drifting, shifting around, sounded like crap listening to SSB.
and the same when I transmitted of course. crap!!!!

so just used it on AM to talk to the locals.

then one day, it would not change frequency. I was always below
channel 1 someplace when I changed the channel switch.

I suspected a problem in the PLL, having a low voltage to the 8719.

I did a google search and found the solution in this WWDX Forum.
Resistor R130 goes bad. it is hidden. got to read the posts on this.
But I replaced it with a quarter watt 10 ohm resister. Now OK!!!!
PLL working, SSB working great, I can turn it on and listen to
all the garbage for hours on ch. 38 LSB! and I can tune into the
garbage stations, with VOICELOCK since they are not all on frequency.

Then I adjusted the TX ALC and AMC all the way off. I was surprised that
this part of the circuit was not all cut off the board! (as usual!)
I can see on the scope that with the DYNAMIKE control turned up to
a certain point, my AM and SSB is not clipping, and just right.
Does not have that delay after the ALC/AMC kicks in.

so there is hope for the "D" made in China version, maybe.
get a new microphone. replace resistor R130 in the PLL circuit.
take out the ass-clown mods.

But they all say I sound good now on this unwanted radio.
yeah, this guy grabbed it and almost shoved it in my face
to give it to me.

.....

 

[Eldorado828]

hey! hold on, hold on, before you destroy another.....

I was "very quickly" given a nice looking but not working "D" radio
about 2 years ago, after asking a local about getting a CB with SSB mode.

View attachment 70633
.
View attachment 70634
.
first problem - no TX modulation, and also receive audio
was scratchy. found that newer big fat ugly Cobra microphone
had a bad element, and the switch contact for receive speaker
audio to be bad. so wired up this older Cobra microphone.

then found the usual MOD, the RF GAIN was modified to adjust
the RF output carrier level. I wired it back to stock, so now I can
lower the receive RF gain to listen to these guys around me having
300 watts and more of over modulated signals.

then what I wanted this radio for, SSB, did not sound very good.
drifting, shifting around, sounded like crap listening to SSB.
and the same when I transmitted of course. crap!!!!

so just used it on AM to talk to the locals.

then one day, it would not change frequency. I was always below
channel 1 someplace when I changed the channel switch.

I suspected a problem in the PLL, having a low voltage to the 8719.

I did a google search and found the solution in this WWDX Forum.
Resistor R130 goes bad. it is hidden. got to read the posts on this.
But I replaced it with a quarter watt 10 ohm resister. Now OK!!!!
PLL working, SSB working great, I can turn it on and listen to
all the garbage for hours on ch. 38 LSB! and I can tune into the
garbage stations, with VOICELOCK since they are not all on frequency.

Then I adjusted the TX ALC and AMC all the way off. I was surprised that
this part of the circuit was not all cut off the board! (as usual!)
I can see on the scope that with the DYNAMIKE control turned up to
a certain point, my AM and SSB is not clipping, and just right.
Does not have that delay after the ALC/AMC kicks in.

so there is hope for the "D" made in China version, maybe.
get a new microphone. replace resistor R130 in the PLL circuit.
take out the ass-clown mods.

But they all say I sound good now on this unwanted radio.
yeah, this guy grabbed it and almost shoved it in my face
to give it to me.

.....

I've got one just like your photo in pristine condition but I've never given it a chance because of the bad publicity they've had.

Maybe I should break it out and give it a shot.

 

[Pez]

This is what I did to one of mine. Works great on 10m SSB now.

I have some others that I haven't touched, they are very poor on SSB. I will have a look at R130 and the other post with all that info, and see how that goes. Cheers!

 

[BayouRadioAmplifier]

Help needed for Cobra 148 NW ST

Okay, Apparently, when this rig went back to Cobra to get Factory Reconditioned, instead of changing out R130 like they should've, it appears the "geniuses" at Cobra installed a Mod consisting of a board labeled: KEPC-635-A, and says: "for 148nw latchup reset." The board consists of 2...

www.worldwidedx.com

read that post. it is the blue wire from that little board as pictured.
it goes to a 10 ohm resistor, to the main board. it needs to be changed to
higher wattage. that resistor fails, and the voltage to the 8719 drifts.
the PLL drifts... My "made in China" "D" version works great now.

 

[BayouRadioAmplifier]

first thing you can do, is power the radio up, and measure
the voltage at the PLL MB8719 IC1 at pin-9 "VDD"
it should be over 8 volts. if this voltage is down to
5 to 7 volts and changing around, this is the problem.
on my radio here it went down to 4.5 volts and the PLL failed.

 

[9C1Driver]

I’m glad you have one working to the point you like it and feel it’s great. That said they are still a very crappy radio. For what the average person would have to pay a tech to make it function better is just not cost effective. There is a thread here on the forum from years ago talking about this. One of the resident techs here listed all the parts that were either eliminated, cheapened up, or compromised on one of these radios. It was just a shame Cobra did this.

 

[nomadradio]

Hey, that's what a warbly SSB radio needs. A DDS. I bought one of those or one like it and haven't tried it out yet. Want to try it with a tube radio.

73

 

[Pez]

Hey, that's what a warbly SSB radio needs. A DDS. I bought one of those or one like it and haven't tried it out yet. Want to try it with a tube radio.

73

It was a fun project on a rainy day! The DDS is actually Arduino based and the original (very basic) sketch can be found online. I had to make changes to the code to make it work the way I wanted, (and I added new step options and changed the button functions around). You can then re-flash it with ISP through Arduino.

This particular DDS VFO has a few limitations, but its fine for this job providing you don't need it to be fully integrated with mode switching, automatic offsets, etc...

If anyone here goes down that path let me know, I can send you my modified sketch (.ino) to save you some time.

73

 

[TM86]

It was a fun project on a rainy day! The DDS is actually Arduino based and the original (very basic) sketch can be found online. I had to make changes to the code to make it work the way I wanted, (and I added new step options and changed the button functions around). You can then re-flash it with ISP through Arduino.

This particular DDS VFO has a few limitations, but its fine for this job providing you don't need it to be fully integrated with mode switching, automatic offsets, etc...

If anyone here goes down that path let me know, I can send you my modified sketch (.ino) to save you some time.

73

I'm always interested in DDS VFO projects. I like to compare against what I've already done and see what ideas I've failed to steal.

 

[Pez]

It's such a basic VFO that there might not be much that is worth stealing! hihi. My modified .ino is attached.

The code is for this style of DDS VFO: https://www.ebay.com/itm/2966370344...pid=5336136228&customid=&toolid=10001&mkevt=1

 

[TM86]

It's such a basic VFO that there might not be much that is worth stealing! hihi. My modified .ino is attached.

The code is for this style of DDS VFO: https://www.ebay.com/itm/2966370344...pid=5336136228&customid=&toolid=10001&mkevt=1

True enough, but you never know where an idea might come from. For instance, the bar graph code has triggered a thought of how to cram all the needed info into the space of a typical mobile meter for adding DDS VFO capabilities to a 23 channel rig without having to carve up the faceplate. Don't know that I'll ever do it, but it is a fun mental exercise.