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Cobra 19 GTL Mods
- Thread starter Rc123
- Start date
Pretty easy. Put a transistor instead of D10.
R - sets minimum DK limit. TR- BD911 or any NPN 3A+ transistor.
Mike
R - sets minimum DK limit. TR- BD911 or any NPN 3A+ transistor.
Mike
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This will work, but be sure you have a heat sink that's big enough on the power transistor.
The typical way it's done on a Cobra 29 (for example) is to only control the modulated voltage to the driver transistor alone. Controlling the voltage that feeds the driver and final transistors both (like in the diagram) will put more current through the new transistor and increase the heat it must safely unload.
The Cobra 29LTD type radio is really easy because the factory built in a wire jumper on the circuit board that's placed EXACTLY where the new transistor gets added. Remove the jumper, replace it with two wires leading to the new transistor.
This radio won't be that easy to do this way. This circuit board is NOT laid out in a way that would make it easy. You're probably better off with the setup Mike shows above, just for the simplicity. We use a Darlington-type power transistor to reduce the current coming out of the carrier-control pot. Types that are common would be TIP120,121, or 122.
Just don't forget a heat sink.
73
The typical way it's done on a Cobra 29 (for example) is to only control the modulated voltage to the driver transistor alone. Controlling the voltage that feeds the driver and final transistors both (like in the diagram) will put more current through the new transistor and increase the heat it must safely unload.
The Cobra 29LTD type radio is really easy because the factory built in a wire jumper on the circuit board that's placed EXACTLY where the new transistor gets added. Remove the jumper, replace it with two wires leading to the new transistor.
This radio won't be that easy to do this way. This circuit board is NOT laid out in a way that would make it easy. You're probably better off with the setup Mike shows above, just for the simplicity. We use a Darlington-type power transistor to reduce the current coming out of the carrier-control pot. Types that are common would be TIP120,121, or 122.
Just don't forget a heat sink.
73
Last edited: