Cobra 148 GTL mod

[larryb]

You were correct R44 is tied to RX 8V, and that is where I tied it into.

By changing the value to 8.2K and tie it to the same spot I tied VR402 to (8V constant) will effect the voltage and

I did move the orange wire on VR402 to the + side of C84 (8v all the time).

R175 was a 2.2K resistor in series with the other side of VR402 and went to ground. This is back in (not shorted out)

The center wiper of the VR402 had a 22K in series going to junction of R44 and D51 and that is jumped and so is D51.

Both D51 and R174 are jumped out and D52 is clipped out.

With the 8.2K added in from constant 8v to junction R44/D51, I can now swing the voltage at that point. The swing is not a peaky as before .

Clarifier knob is centered and reception of channel 19 is good. I can swing channel 19 off center both ways. How much I dont know but with the clarifier fully clockwise I can hear some channel 19 traffic on channel 18, but not 19 on channel 20 with VR402 counter clockwise. So the swing is more in one direction than the other.

I think it will work ok this way.

Thanks for sticking it out.

There is a CB repair shop at one of the truck stops on the interstate , I think I will take the radio there and have them check the freq swing for me.


Larry

 

[Toll_Free]

If it is a GOOD shop, they SHOULD be able to center slot the clarifier for you.

I've ALWAYS, on EVERY radio I've EVER done, center slotted the clarifier. To do anything else is just friggin GHETTO.

No problem on sticking it out. I'd like to find the difference in the chassis, so we can maybe make a sticky for people.

Sounds like the divider is JUST about right, just a little to one side or another. This CAN happen, as the (both tx and rx) full 8 volts is sometimes SLIGHTLY different than the RX only.

I need a STOCK 148 chassis to do, then I could give step by step, rather than 'by the schematic' instructions. As we've BOTH seen, radios change, even with the same model number.

Glad to see you've got it nearly straightened out. If you have center on center, I'd be happy.... As I've said, EVERY chassis I do is center slot, ON CENTER SLOT. Then they go DOWN about 11.5 kC and up about 6. This gives you EVERY possible combination.

--Toll_Free

 

[Robb]

Congrats on getting it right!

I'd like to see this mod for a newer 148 that doesn't slide sooo much. Perhaps 500 or so per side. When they slide that much - it's hard to use it. That is; a little doesn't move too far . . .

 

[74IN]

Unless you are using a freq counter, don't unlock the clarifier. The clarifier will zero at different locations on the dial when the ambient temperature changes.
As far as R131 goes, that'll only open up AM....there is a variable pot on the board to open up the ssb. Cobra 148s sound great with the limiter clipped.....most exports don't.

As all do, RX and TX, locked or unlocked. A frequency counter won't change that a bit. One also won't tell you where the other guy is. Adjustment is by ear at any temp.

 

[Robb]

Congrats on getting it right!

I'd like to see this mod for a newer 148 that doesn't slide sooo much. Perhaps 500 or so per side. When they slide that much - it's hard to use it. That is; a little doesn't move too far . . .

 

[larryb]

I found this link for the service manual of the Texas Ranger TR-296GK/DX

http://www.rangerusa.com/pdf/man296.pdf

This unit is a Ranger, (Malaysia) renamed as a Cobra 148

I did a search for my PCB model (EPT014813Z) and this popped up. Looking at the service manual the PCB layout is marked EPT014811Z, but in the parts listing the board is called out as a EPT014813Z.

This manual shows that this unit had a freq counter plug on the back side of the unit. Other than that it looks just like mine.

I checked both my board and this document for part locations and numbers on the board (not every one of them but a fair share) and they seem to be identical. My board (EPT014813Z) has some parts that were not installed but the silk screen and etching are there. Maybe this was for the freq counter components??

Anyway, for those that have this unit you may wish to down load and save this manual for reference...

Thank God for the internet and Google search

Larry

 

[Toll_Free]

Congrats on getting it right!

I'd like to see this mod for a newer 148 that doesn't slide sooo much. Perhaps 500 or so per side. When they slide that much - it's hard to use it. That is; a little doesn't move too far . . .

By NOT jumping D51 and R174, you have the mod that will give you an unlocked clarifier, and at the SAME time give you stock slide, about a kc up and down, give or take (each chassis slides a bit differently).

The problem we had here was that pesky R44 and me forgetting to tell him to bring it to +8 volts constant.

BUT, that's your mod.

Red wire from clarifier to 8 volts constant
Cut D52
Lift end of R44 going to 8 volts on RECEIVE and put it to 8 volts constant.

Go enjoy talking DX, you have a stock range clarifier that tracks on tx and rx.

For those wanting MAX slide,

Remove R44 and throw it in the junkpile
Jumper R174
Jumper R175
Jumper D51

This will give app 18 kc, give or take, of slide.

Feel free to make this a sticky, might be good reference for those wanting to learn how to unlock, or those wondering why when they get their radio back "unlocked", all of a sudden their clarifier became a VFO. Also, this can help people put their radios back to STOCK, or if you really want to, play with the values of R44, R174 and R175 and then you can custom tailor a clarifier.

--Toll_Free

 

[jazzsinger]

i've never understood why anyone would need more than +/- 5khz slide, with that you can go anywhere between any 2 cb channels except the 5 alpha channels, even if you want to cover them you only need 10 khz slide max.

in my experience another reason slide like that is undesireable is the radio's that slide the most tend to drift the most too, which on AM/FM may not be a serious issue, but can be a nightmare on ssb.

there is much merit on clarifiers that slide on tx/rx, but it really depends on who is using the radio, in inexperienced hands it becomes a game of chase me, chase me, very quickly, especially if the user has ego issues and has got it into his head that his radio is the frequency standard all others should be judged by, (far more people are like that than you might realise at first),

it never ceases to amaze me how often i hear guys telling others they are off frequency, the irony in most cases are a lot of them are using radios that are all over the place or using radios that have a frequency display rather than a true frequency counter, but you just can't tell them.

if i can hear you clearly on ssb then it don't matter what any display/counter says, all that matters is that we are both on the same frequency irrespective of what it actually is.

 

[Low_Boy]

Toll_Free ...every body has there own opinion so I may get a million different answers but what is the ideal amount of slide. I hope I have not opened up a pandoras box.

 

[larryb]

I dont think it is the amount of slide that counts, its how you use it. As stated sometime you play the game of catch me when you over use the slide too much.

Back when I used to talk skip on channel 16, you could hear a dozen stations all on top of each other . With a slide I would just adjust the clarifier to say 1 or 2 O'clock off center and start calling. If someone else have a slider they could get onto you and reject the others that were on center freq.

If you had little patience you would move it again, the other person that may be trying to talk to you would have to chase you.

My method was I would move the clarifier off center and stay there. I got alot of QSL cards just doing that.

Just my $.02 worth.

Larry

 

[1iwilly]

The problem we had here was that pesky R44 and me forgetting to tell him to bring it to +8 volts constant.

BUT, that's your mod.

Red wire from clarifier to 8 volts constant
Cut D52
Lift end of R44 going to 8 volts on RECEIVE and put it to 8 volts constant.

--Toll_Free

hey toll been a long time ok i have a 148 made in philly when i lift the end of r-44 do i still need to use a 800ohm resister.??going to it.??or the 8+volts go directly to it or do i change r-44 to 800ohms.?? thanks

 

[Toll_Free]

hey toll been a long time ok i have a 148 made in philly when i lift the end of r-44 do i still need to use a 800ohm resister.??going to it.??or the 8+volts go directly to it or do i change r-44 to 800ohms.?? thanks

At THIS point I'm saying LEAVE R44 whatever value is in YOUR radio. The thing to do is ensure you take the 8 volt side of it, and put it to the constant 8 volts.

I BELIEVE that the difference in values can be attributed to either a different value of clarifier pot, OR it could be the used a different 'taper' in some chassis (read this as, they used whatever they could source cheapest). BUT, the fact remains, it's part of the voltage divider, so I'd leave it at it's ORIGINAL value in YOUR radio, then just move the necessary side to constant 8.



To the gentleman asking about the IDEAL amount of slide, that depends: If you have a radio with a 10Khz or +10 or 10Kc jump in it, then about 7.5 to 8 is ideal for me. 6 down and 2 up will get you ANYONE.

If you DON'T have the 10k switch, then I like to go down 11, and up about 4. I can control a radio like this, and for those that have fatfingers you can always fine / course. ANOTHER thing you can do is do a single control for TX/RX locked together, then on the other (using a dual pot like the 2000 does), do a RX ONLY clarifier. This way when you find someone who always is twiddling the control, you let them do their dance, then can slide to them to get the best quality out of your radio.....

Also, this isn't ALWAYS a problem with attitudes, if your carrier injection is off, you'll do that dance forever, as the incoming signal IS off, but it's off in YOUR passband

--Toll_Free

 

[Low_Boy]

Thank you. There is a lot to learn, You must have been doing this for a while because you really know what you are talking about. And you really know the schematics also.

 

[Toll_Free]

Thank you. There is a lot to learn, You must have been doing this for a while because you really know what you are talking about. And you really know the schematics also.

I started taking Bill Good and Bill Cheek equipment apart in the 80s. Also was 'friendly' with some of the people involved in Messenger, when they first came out.

The gentleman that was techsupport@galaxyradios.com (Ray) for a LONG time was also my mentor.... He has a HELL of a station, if he'd ever fire the thing up again

Thanks for the kind words. Once you learn HOW a chassis operates, it's fairly easy to continue taking that to other chassis: BUT, I do specialize in the 8719 Uniden chassis, single and double conversion.


--Toll_Free

 

[Moleculo]

I started taking Bill Good and Bill Cheek equipment apart in the 80s.

If you learned from Bill Good, you learned the right way. That man was an absolute genius when it came to ANYTHING radio related.