Can RF finals be "partially" shot? I have an NTE342 RF final in a transmitter that is not putting out full rated power (only 3 watts but should be more like 6 watts) - Testing the transistor with a diode setting on my meter shows that its okay, but I am wondering if it could still be partially damaged. I am wanting to rule out the possibility thats its been damaged by heat in my clumnsy attempt to install it!
Transistor partial failure possible?
Apr 12, 2005
7 Replies
Possible but remote and your symptoms indicate a different fault.
N
It sure is possible, and is known as 'low gain' or 'low beta'. Diode check wont tell you a transistors gain. You need to put it on a curve tracer and compare the curves for a range of given base current to a known good NEW identical transistor to see the difference.
If I were you I would not use the NTE , and get the original number transistor that was in there. The NTE replacements dont always match the characteristics of the original 100% in detail, and certain differences can cause it to run hotter than normal, and in the long run, reduce its gain. Its also possible not enough heat sink compound was used, and other possibilities too.
what was the original transistor part number
what frequency are you operating at
are the leads all very short, especially the emitter lead
Mark
1/ Substitutions are often "iffy" with RF devices. 2/ Some RF power transistors have multiple emitters and it's possible to lose some of them which degrades performance.
Den Tue, 12 Apr 2005 13:52:42 -0700. skrev Mike:
Try to tune the coil in output circuit. The replacement has possibly not the same capacitance , as the original one.
P.S. I don't know the circuit, just my 0.5$
Med venlig hilsen
Christian Treldal
Sure, happens all the time. I've seen a bunch of 450 MHz finals that look just fine on a curve tracer, but fail to output at 450 MHz.
I've given up trying to test RF transistors at DC or thereabouts. mike
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