K2 pwr amps
Posted by
MARY HAYS CARNEY on
Dec 04, 2007; 10:05pm
URL: http://elecraft.85.s1.nabble.com/K2-pwr-amps-tp456354.html
I have tracked down some of my problems with the K2 transmitter, namely R49 that was not soldered. Now I'm faced with the problem of very low output rf power. I see unbalanced rf voltages at the bases of Q7 and Q8; I.e 0.20 v (rms) at the base of Q7 and 6.6 v (rms) at the base of Q8. I have rewound T2, T3 and T4 and checked that the resistors and rfc chokes in the base circuits of Q7 and Q8 are correct. Also the dc voltages at the base of Q7 and Q8 are both 0.6 v. The dc resistances measured at these transistors are somewhat lower that indicated by the manual: 450 ohms from base(+) to either collector(-) or base(-). With reverse polarity, the base to collector is
> 3000 ohms and the base to emitter resistance is abt 750 ohms.
I suspect that Q7 and/or Q8 are bad. During construction I may have cooked one. If so, should both be replaced, I.e. does Elecraft supply them as a matched pair?
j carney
KB3FBR
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