I have like many others have always been a big fan of the cobra 148 gtl.However i recently traded for the new 148 china made model and was surprized at the lack of sensitivity compared to earlier models.I decided to find the problem and after poking around for hours and looking at the schematic i found the problem,its R67 just to the left of L3.If you want to see a huge improvement jump this resistor with a peice of wire,and i have found no ill effects of this mod just much better gain.Remember this is for the china version only..Enjoy & 73's
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
New to the group with mod
- Thread starter n4dxx
- Start date
IS the schematic on this radio the same or similar to the older 148's?
If so; you might want to check out the Grant XL receive mods
Shottkey diodes, different receive transistor..
http://www.worldwidedx.com/tech-repair/23680-how-perform-2sc2999-schottky-diode-swap.html
Welcome to the forum!
If so; you might want to check out the Grant XL receive mods
Shottkey diodes, different receive transistor..
http://www.worldwidedx.com/tech-repair/23680-how-perform-2sc2999-schottky-diode-swap.html
Welcome to the forum!
Thanks,I had thought about that mod but i really did not think that the cause of this weak reciever was the transistor or the diodes because the older model stock was running loops around the china version,Had it beat bad on rx.I don't know why they didn't use a much less value resistor (R67) for a bit more gain.Now i am happy with the radio...just shunt it out with a wire or hook it to a switch and have a very good (Pre Amp)Though i would not recommend that as it could introduce noise into the rx..But may be worth a shot..
Have you tried this radio on ssb yet?
If not you will be disapointed.
Not very stable due the the 8 volt regulator circuit.
If not you will be disapointed.
Not very stable due the the 8 volt regulator circuit.
Gonna give it a try,I read some about it being very unstable..Did the clarifier mod not sure if that will help..Maybe we can come up with a fix for the drift..any ideas?
The problem is they did away with the 5 pin regulator ic. It was mounted on the side rail. Can not remember the number at the moment. When they had these built they cut cost. Did away with the 5 pin regulator and installed a standard 3 pin 8 volt regulator. On ssb the voltage changes and causes ssb to distort.
I sold the last of the new ones I had so never got around to finding a fix.
i think the cure for this SSB drift is to build a well regulated little zener circuit that powers the clarifier circuit from the 13.8 volt mains.
i have never owned one of these china version 148's so i havent gotten to try out my ideas on one.
i think that will be my next purchase, a chinese 148. that way we can get a complete write up done of this chassis and all that needs to be done to it to bring it up to par.
N4DXX, can you tell if the receiver is the same design they have always used in this chassis? or did they cheap out on it too?
LC
i have never owned one of these china version 148's so i havent gotten to try out my ideas on one.
i think that will be my next purchase, a chinese 148. that way we can get a complete write up done of this chassis and all that needs to be done to it to bring it up to par.
N4DXX, can you tell if the receiver is the same design they have always used in this chassis? or did they cheap out on it too?
LC
Looks basically the same but however i found mine to be deaf as a doorknob compared to the older models,I don't know if it's exactly the same as i am sure it is not,But rest assured if you jump that resistor that i noted the radio's rx will come alive..Can't understand why they would have cut the rx back so much but they did and i found the cure..
you have to remember that quality control in the factories where these radios are made has gone way downhill over the years.
im not sure if you have already done it or not, but i would be sure to give that new radio a complete alignment before you compare it to the old one.
chances are you will pick up at least 2 to 3 S units by simply aligning the receive coils.
LC
im not sure if you have already done it or not, but i would be sure to give that new radio a complete alignment before you compare it to the old one.
chances are you will pick up at least 2 to 3 S units by simply aligning the receive coils.
LC
I've not had an opportunity to mess with one of these much, only one anyone I know had got rid of it almost immediately.
I do believe the SSB problems might be a bit deeper then regulation though.... The old 148 can be easily made to run stable without the MB3756
I do believe the SSB problems might be a bit deeper then regulation though.... The old 148 can be easily made to run stable without the MB3756