Hi... I did something really stupid the other day, and I'm not sure how to fix it. I'll try and be as specific as possible, hoping that someone (maybe Freecell?) can help me out here.
I have a Cobra XL-450 amplfier that I really like. It has always worked extremely well, until I did something to accidentally fry it the other day.
I have an HF/6 meter radio hooked up to it, and have always run it on 10/11 meters. Recently, after installing a six meter antenna on my roof, I was doing some 6 meter alignment work on my radio in preparation to use it with the new antenna.
Now, I have always been able to run my HF rig right through the Cobra XL-450 on various bands, and at full power (100 watts), just as long as I always remembered to do it with the amplifier power switch turned OFF, since it is STRICTLY a 26-30 Mhz amp. Also, I obviously wouldn't want to ever put 100 watts of power through it with the amp ON. I've always been really careful.
This arrangement has always worked just fine. Unfortunately, after experimenting on six meters the other day, my HF rig suddenly started acting up, and stopped producing power, evidentally because of the SWR protection circuit.
I thought something was wrong with the radio, until I noticed that the Cobra amplifiers power light and transmit light was coming on when I would key up the radio, even though the Cobra amplifier was off! It was then that I realized that the SWR on the radio was out the roof! I took the amp out of line, and the SWR went totally back to normal on the radio, so it is DEFINITELY the amp that is blown.
This had never happened before. I had always been able to run 100 watts through it, and on any band I want, but THIS time something popped, and I quickly realized WHY.
Normally, I turn off BOTH the amplifier power switch when not in use, as well as the power supply that runs it. This time, I realized that I had ONLY turned off the power supply switch, but had LEFT ON the amplifier power switch. So, even though the amplifier had no power to it, I was running a 51 Mhz signal through the 28 Mhz amp, WITH the circuit completed, even though the amp was receiving no power from the power supply.
I have always been able to run 100 watts through it, even with the AMPLIFIER power switch on, just as long as the power supply switch was OFF. The only difference THIS time, was that I was running an out of band frequency through it as well.
If I had not had forgotten to turn off the power switch on the amplifier, instead of ONLY on the power supply, this would not have happened. But the switch on the amp completed the circuit, even when the amp had no power.
I know that I have probably made this rather confusing, so let me condense it down to this:
If a person ran 51 Mhz into a 28 Mhz amp (with no power to the amp), and the amp fried as a result, what would be the thing to look for? A blown transistor? Diode? Capacitor?
I have tested all the resistors inside. I have an identical amp, and set them side by side to compare the resistor values. They are all good. However, there IS a burnt smell inside the blown amp, and there isn't in the non-blown amp. So SOMETHING did fry.
It's not the finals, because the amp was not even receiving power, and was not dissipating any wattage. So what is it that goes wrong from putting an out of band signal through it?
What do I look for?
I truly hate to just throw away a really great amp.
Help?
I have a Cobra XL-450 amplfier that I really like. It has always worked extremely well, until I did something to accidentally fry it the other day.
I have an HF/6 meter radio hooked up to it, and have always run it on 10/11 meters. Recently, after installing a six meter antenna on my roof, I was doing some 6 meter alignment work on my radio in preparation to use it with the new antenna.
Now, I have always been able to run my HF rig right through the Cobra XL-450 on various bands, and at full power (100 watts), just as long as I always remembered to do it with the amplifier power switch turned OFF, since it is STRICTLY a 26-30 Mhz amp. Also, I obviously wouldn't want to ever put 100 watts of power through it with the amp ON. I've always been really careful.
This arrangement has always worked just fine. Unfortunately, after experimenting on six meters the other day, my HF rig suddenly started acting up, and stopped producing power, evidentally because of the SWR protection circuit.
I thought something was wrong with the radio, until I noticed that the Cobra amplifiers power light and transmit light was coming on when I would key up the radio, even though the Cobra amplifier was off! It was then that I realized that the SWR on the radio was out the roof! I took the amp out of line, and the SWR went totally back to normal on the radio, so it is DEFINITELY the amp that is blown.
This had never happened before. I had always been able to run 100 watts through it, and on any band I want, but THIS time something popped, and I quickly realized WHY.
Normally, I turn off BOTH the amplifier power switch when not in use, as well as the power supply that runs it. This time, I realized that I had ONLY turned off the power supply switch, but had LEFT ON the amplifier power switch. So, even though the amplifier had no power to it, I was running a 51 Mhz signal through the 28 Mhz amp, WITH the circuit completed, even though the amp was receiving no power from the power supply.
I have always been able to run 100 watts through it, even with the AMPLIFIER power switch on, just as long as the power supply switch was OFF. The only difference THIS time, was that I was running an out of band frequency through it as well.
If I had not had forgotten to turn off the power switch on the amplifier, instead of ONLY on the power supply, this would not have happened. But the switch on the amp completed the circuit, even when the amp had no power.
I know that I have probably made this rather confusing, so let me condense it down to this:
If a person ran 51 Mhz into a 28 Mhz amp (with no power to the amp), and the amp fried as a result, what would be the thing to look for? A blown transistor? Diode? Capacitor?
I have tested all the resistors inside. I have an identical amp, and set them side by side to compare the resistor values. They are all good. However, there IS a burnt smell inside the blown amp, and there isn't in the non-blown amp. So SOMETHING did fry.
It's not the finals, because the amp was not even receiving power, and was not dissipating any wattage. So what is it that goes wrong from putting an out of band signal through it?
What do I look for?
I truly hate to just throw away a really great amp.
Help?
