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Hi, I'm new to the forum. There seems to be a lot of people here with experience of RF power amplifiers and I was hoping someone might be able to give me some pointers.

I have an amplifier which is not working properly. With 10W going in it should output 125W (as compared to a working amp) this one isn't, it's only putting out around 20-50W. One thing I noticed is that the input SWR is very high, like 5:1. With 1W going in the SWR is ok, but at 10W input swr is very high. I find it strange that the input swr increases as the input power increases. For reference, input swr on a working amp is 1.5:1 with the same 10W applied.

Both output transistors have been replaced (old ones confirmed dead), switching relay has been replaced. Bias and collector voltages are present. I've pulled out and tested every single other semiconductor in the circuit. With reference to the circuit diagram (attached) I removed C1 and D10 which isolated everything except the amplifier part. Still get the same problem.

I'm at a loss now as how to even fault find it. it looks like a problem somewhere with the matching circuit perhaps ?

<blockquote data-quote="TheWookie" data-source="post: 757347" data-attributes="member: 60609">Hi, I&#039;m new to the forum. There seems to be a lot of people here with experience of RF power amplifiers and I was hoping someone might be able to give me some pointers.I have an amplifier which is not working properly. With 10W going in it should output 125W (as compared to a working amp) this one isn&#039;t, it&#039;s only putting out around 20-50W. One thing I noticed is that the input SWR is very high, like 5:1. With 1W going in the SWR is ok, but at 10W input swr is very high. I find it strange that the input swr increases as the input power increases. For reference, input swr on a working amp is 1.5:1 with the same 10W applied. Both output transistors have been replaced (old ones confirmed dead), switching relay has been replaced. Bias and collector voltages are present. I&#039;ve pulled out and tested every single other semiconductor in the circuit. With reference to the circuit diagram (attached) I removed C1&nbsp; and D10 which isolated everything except the amplifier part. Still get the same problem. I&#039;m at a loss now as how to even fault find it. it looks like a problem somewhere with the matching circuit perhaps ?</blockquote>

[QUOTE="TheWookie, post: 757347, member: 60609"] Hi, I'm new to the forum. There seems to be a lot of people here with experience of RF power amplifiers and I was hoping someone might be able to give me some pointers. I have an amplifier which is not working properly. With 10W going in it should output 125W (as compared to a working amp) this one isn't, it's only putting out around 20-50W. One thing I noticed is that the input SWR is very high, like 5:1. With 1W going in the SWR is ok, but at 10W input swr is very high. I find it strange that the input swr increases as the input power increases. For reference, input swr on a working amp is 1.5:1 with the same 10W applied. Both output transistors have been replaced (old ones confirmed dead), switching relay has been replaced. Bias and collector voltages are present. I've pulled out and tested every single other semiconductor in the circuit. With reference to the circuit diagram (attached) I removed C1 and D10 which isolated everything except the amplifier part. Still get the same problem. I'm at a loss now as how to even fault find it. it looks like a problem somewhere with the matching circuit perhaps ? [/QUOTE]

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