The Cobra 200GTL-DX problems

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Unit 67
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Joined: Thursday 3rd Mar 2005, 11:26
Location: Puerto Rico

The Cobra 200GTL-DX problems

Post by Unit 67 »

Hi at all;I have in my shop 9 Cobras 200GTL-DX with the TX power problem in the Hi Position.I founded the problem."A bad Driver transistor".The driver part number is #RD16HHF1.I make a call at the Cobra service department,because this part does not have any replacement.The original Cobra part number is #010-133.The part number in the board is the Q73.I founded couple of errors in the schematic of this radio too.In the schematic the driver transistor is the Q74,but the correct part number is the Q73,not the Q74.The schematic diagram for this radio has a lot of errors.The prediver in this radio is the KTC2078.If this number is familiar for you, is correct.This is the same transistor used in the old radios.,but with the exception of the first three letters.Hmmmmm!!!!!!!!!! :? About the driver transistor,there it is a piece of Junk part.I am going to use Mitsubishi part number 2SC3133 instead of the junk part number RD16HHF1.I did a test in one of the RD16HHF1 transistors.The results in my transistor tester are:A gain of just 58% at 5.0 volts,and just 45% at 13.0 Volts."This is incredible".





73sss... Unit 67-Puerto Rico
butch
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Cobra 200 gtl dx

Post by butch »

I just bought a new Cobra 200. It works great on the high band. Swr 1.3. When I hit my amp swr 1.4-5. The problem is this drives my amp too hard(about 750 to 800 watts). When I hit the amp on low power with about 8 watts the swr goes out the roof but will modulate backwards to 1.8-2.4. The swr on the low side with out the amp is 1.2. Can anyone tell what I need to do since I dare not run the radio on high with the amp..
Unit 67
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Joined: Thursday 3rd Mar 2005, 11:26
Location: Puerto Rico

Post by Unit 67 »

This is a very usual problem in this radio.For example:If your radio has the peak Mod when you push the power swich at the Hi power position,the RF meter in the radio shows the RMS power,not the PEP power and the radio shows an incorrect SWR readings.But in the Lo power position,the RF and the SWR meter works correct.I have one question: What kind of amplifier you have?






73sss... Unit 67-Puerto Rico
haans_gruber
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Joined: Thursday 27th Jul 2006, 7:07
Location: Freehold, Terra Libra

Re: Cobra 200 gtl dx

Post by haans_gruber »

butch wrote:I just bought a new Cobra 200. It works great on the high band. Swr 1.3. When I hit my amp swr 1.4-5. The problem is this drives my amp too hard(about 750 to 800 watts). When I hit the amp on low power with about 8 watts the swr goes out the roof but will modulate backwards to 1.8-2.4. The swr on the low side with out the amp is 1.2. Can anyone tell what I need to do since I dare not run the radio on high with the amp..
The SWR should be read by an external SWR meter between the amplifier and the antenna in order to get an accurate reading.

Try using a dummy load to test the match between the radio and the amplifier.

The radio is a known 50 ohms, the amplifier is also a known 50 ohm impedance, this leaves only the antenna to be a mismatch. Coax is mirror of what it sees on either end of it.

peace,

haans :)
haans_gruber
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Joined: Thursday 27th Jul 2006, 7:07
Location: Freehold, Terra Libra

Re: The Cobra 200GTL-DX problems

Post by haans_gruber »

Unit 67 wrote:Hi at all;I have in my shop 9 Cobras 200GTL-DX with the TX power problem in the Hi Position.I founded the problem."A bad Driver transistor".The driver part number is #RD16HHF1.I make a call at the Cobra service department,because this part does not have any replacement.The original Cobra part number is #010-133.The part number in the board is the Q73.I founded couple of errors in the schematic of this radio too.In the schematic the driver transistor is the Q74,but the correct part number is the Q73,not the Q74.The schematic diagram for this radio has a lot of errors.The prediver in this radio is the KTC2078.If this number is familiar for you, is correct.This is the same transistor used in the old radios.,but with the exception of the first three letters.Hmmmmm!!!!!!!!!! :? About the driver transistor,there it is a piece of Junk part.I am going to use Mitsubishi part number 2SC3133 instead of the junk part number RD16HHF1.I did a test in one of the RD16HHF1 transistors.The results in my transistor tester are:A gain of just 58% at 5.0 volts,and just 45% at 13.0 Volts."This is incredible".





73sss... Unit 67-Puerto Rico
Problem here is one is an FET and one is not. I do not believe they cross.

peace,

haans :)
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