Way good stuff here ! You want to be louder on AM on a 148GTL type chassis ? As stated ...leave TR24 alone ! (unless you want to screw up SSB) you can clip R131 and make your radio louder on AM and you can there after control it by the mic gain on the radio ......Is it a perfect science ? No ! , does it hurt SSB ? No ! ..........You also have a diode/resistor mod that will basically do the same thing ..........Is it also a perfect science ? No ! Do they work ? Yes ! .........I truly get what the O-Scopes and Analyzers are telling me and it surely can be a beautiful thing .........but in the end .............I don't talk to machines , I talk to people ............it's usually them that break me or make me . (Much respect to Handy and Nomad and others to take the time of there days to explain the theory's and relativities of the truth of the matters on all of this) .......I'm nothing more then a hobbyist for the last 40 years and now with the Internet and You tube and what not , you too can be that much more a know it all hobbyist (I truly believe I was honored with a Golden Screw Driver Award a long time ago) Switch Kit
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Cobra 148gtl r131 removal?
- Thread starter groundwire
- Start date
you can always have the option of putting R131 on an off and on a toggle switch
Umm.. Specs?
Repairing an unknown failure has more to do with finding the cause of the fault, and less to do with a specification.
The phrase "still no transmit" makes it sound as if it were not transmitting before the RFX was removed. You have accomplished one step of troubleshooting, though. You know the RFX wasn't the whole problem. It might be bad, might be good. Can't tell now.
What tools do you have to work with? A radio that won't transmit is a lot like "my car won't start". Sure it's one simple symptom. But more than one fault can cause it.
First thing to find out is if the LED on the front panel changes from green to red when you key the mike.
If it does, at least we know the switching circuits are not dead.
Do you have another radio you can tune to the same channel? If so, attach a coax jumper to it and back off the shell down the cable. This makes the center pin into a 'sniffing' antenna.
Set both radios to the same channel and key the mike on the 148. Can you hear anything? If not, hold the end of the coax jumper near the transmit circuits and see if you get anything that way.
What to do next depends on what you discover this way.
73
Repairing an unknown failure has more to do with finding the cause of the fault, and less to do with a specification.
The phrase "still no transmit" makes it sound as if it were not transmitting before the RFX was removed. You have accomplished one step of troubleshooting, though. You know the RFX wasn't the whole problem. It might be bad, might be good. Can't tell now.
What tools do you have to work with? A radio that won't transmit is a lot like "my car won't start". Sure it's one simple symptom. But more than one fault can cause it.
First thing to find out is if the LED on the front panel changes from green to red when you key the mike.
If it does, at least we know the switching circuits are not dead.
Do you have another radio you can tune to the same channel? If so, attach a coax jumper to it and back off the shell down the cable. This makes the center pin into a 'sniffing' antenna.
Set both radios to the same channel and key the mike on the 148. Can you hear anything? If not, hold the end of the coax jumper near the transmit circuits and see if you get anything that way.
What to do next depends on what you discover this way.
73
The following items are a must for working on any radio
1. Service Manual and Schematic
2. Frequency Counter
3. Volt Meter (Multi Meter)
4. Oscilloscope
5. Soldering Tools and Solder
1. Service Manual and Schematic
2. Frequency Counter
3. Volt Meter (Multi Meter)
4. Oscilloscope
5. Soldering Tools and Solder
TinySA can fill the gap here until you can afford something better.
Hi guys. I know this is an old post. I have 2 x Cobra 148 GTL (Taiwan) with the mic on the side and wanted to increase my modulation. All I did was solder a 10K resistor across R126 (10K as well. That gives me +- 5K). My first attempt didn't work as I used a 1.2K resistor. Got really crappy audio reports. I don't remove TR24 or snip R131 (also a 10K). I just solder a 10K resistor across R131. Audio reports beautiful, no splattering. 
Off the topic here. Anyone have an image of the original Cobra 148 GTL Microphone insert? The one I am using is a 500 ohm (obviously) Dynamic with the plastic diaphragm or whatever it is called. Never actually had an original Cobra Mic accept the Casing. Help would be appreciated. Also, my image I have to change as I am 57 now. Don't look that young. 73 from Cape Town. 18:14 Pm and have to go and see to my German Shepherds and 2 pigeons.
