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Originally Posted by G0HZU_JMR
Neat analysis! Could this explain some of the subtle differences we see in the bias board? What about the blue marks in the resistance sections seen on the bias board. Is this some sort of thermal stress or could it be stress from the horrible absorber glue? At one point I thought the blue marks might be a by product of trimming the resistance at the factory but I'm not sure the resistances need to be very accurate.
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In my case it can explain that R5 is a bit higher than yours. Some gold is missing in between R5 and the PNP emitter. The resistors R5 and R2 are most important to set the RF transistor current and collector voltage if you assume that the divide ratio of R3 and R4 is correct. I think that the resistors are not trimmed. It is a pity that the documentation is missing of this IF1 block. It is also possible that there is some difference between series of the TR4172. How can I find out which year mine is?
Regards, Lex