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Discussion in 'Amplifiers' started by Nick454, Nov 13, 2018.
Can someone tell me why these resistors are heating up?
Unfortunately this usually means at least one of the output transistors has blown open. These larger resistors are balancing resistors and if all 6 transistors are making equal power, no RF power would be across these resistors. As soon as one transistor stops working, the unbalanced RF builds up across those resistors and smokes them.
When this happens, these are not the only resistors that usually burn up. Look around the bottom of each "pill" for a smaller, 10 ohm swamping resistor. You are likely to see at least one of these is burnt also and that means the transistor right next to it is burnt too. Lots of other things can cause this from bad capacitors to solder blobs shorting things out but this is the first place to start looking.
Thank you I've replaced the resistors that were burning and they are still getting hot. I'm not seen anything else burning but I've noticed my audio coming across the board when I talk more than I have ever have. I'm wondering if this has to do with a bad output transistor.
Found a bad solder joint!
nick454, your question about possible bad output transistors has already been answered.
the answer is yes, you probably have one or more blown transistors.
Make sure the lands - your "islands" - are not too full of solder that drips down onto the backplane.
If your amp sounds like it has built in talk back then you are kicking it's butt. If it is louder now then the bias might need some help.
Hearing your audio from inside the amp is from the output transformers. Either the output is out of tune on one or more stages, you have a weak transistor and it can also be caused by harmonics. A dirty radio or possibly being over driven.
If your bad solder joint wasn't the issue it's time to start testing transistors and capacitors. The resistors on the combiner are burning because there is an imbalance. One or more sections are weaker than the other for any number of reasons. Testing the individual components is the only way to find the issue.