You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

Thanks for the replies.

I made sure to replace the failed transistors with the same make and model (Toshiba 2SC2782) and I made sure to buy a matched pair too.

Only reason I detatched C1 was just to isolate that part of the circuit and eliminate it from being the cause of the problem. Hopefully it narrowed down the problem area a bit.

I have been driving this into a high power dummy load, I did measure the output VSWR, can't remember if it was skyhigh or not on the output. Nothing looks to be overheated or burnt out.

So it's looking like there is a failed cap somewhere. I didn't think to check the temp of the transistors, I will do that and see if one is getting hotter than the other. I didn't want to keep running it in fault condition in case it damages the new replacement output transistors. This amp is designed to take up to 50W input so I guess testing at 10W is ok ?

Regards the gain, I tested a working unit on the bench with a signal generator and low pass filter into a 50ohm dummy load. I put an insertion type power sensor on the input and output. With 10W in it put 125W out. At 50W in it made 195W out. From what I have read these amps seem a bit variable in quality, some people get 200W out with only 30W input.

<blockquote data-quote="TheWookie" data-source="post: 757568" data-attributes="member: 60609">Thanks for the replies.I made sure to replace the failed transistors with the same make and model (Toshiba 2SC2782) and I made sure to buy a matched pair too. Only reason I detatched C1 was just to isolate that part of the circuit and eliminate it from being the cause of the problem. Hopefully it narrowed down the problem area a bit. I have been driving this into a high power dummy load, I did measure the output VSWR, can&#039;t remember if it was skyhigh or not on the output. Nothing looks to be overheated or burnt out. So it&#039;s looking like there is a failed cap somewhere. I didn&#039;t think to check the temp of the transistors, I will do that and see if one is getting hotter than the other. I didn&#039;t want to keep running it in fault condition in case it damages the new replacement output transistors. This amp is designed to take up to 50W input so I guess testing at 10W is ok ? Regards the gain, I tested a working unit on the bench with a signal generator and low pass filter into a 50ohm dummy load. I put an insertion type power sensor on the input and output. With 10W in it put 125W out. At 50W in it made 195W out. From what I have read these amps seem a bit variable in quality, some people get 200W out with only 30W input.</blockquote>

[QUOTE="TheWookie, post: 757568, member: 60609"] Thanks for the replies. I made sure to replace the failed transistors with the same make and model (Toshiba 2SC2782) and I made sure to buy a matched pair too. Only reason I detatched C1 was just to isolate that part of the circuit and eliminate it from being the cause of the problem. Hopefully it narrowed down the problem area a bit. I have been driving this into a high power dummy load, I did measure the output VSWR, can't remember if it was skyhigh or not on the output. Nothing looks to be overheated or burnt out. So it's looking like there is a failed cap somewhere. I didn't think to check the temp of the transistors, I will do that and see if one is getting hotter than the other. I didn't want to keep running it in fault condition in case it damages the new replacement output transistors. This amp is designed to take up to 50W input so I guess testing at 10W is ok ? Regards the gain, I tested a working unit on the bench with a signal generator and low pass filter into a 50ohm dummy load. I put an insertion type power sensor on the input and output. With 10W in it put 125W out. At 50W in it made 195W out. From what I have read these amps seem a bit variable in quality, some people get 200W out with only 30W input. [/QUOTE]

Top Bottom