New KX1 low power and 20m oscillation

Posted by Stan Gibbs, KR7C on May 05, 2012; 10:54pm
URL: http://elecraft.85.s1.nabble.com/New-KX1-low-power-and-20m-oscillation-tp7531133.html

Just finished building the KX1 and the transmit testing is not going well. My only bench tool is a DVM.


Power supply is a 13V battery.  Ant is a 50 ohm dummy load. The receiver seems to work fine.  All DC voltages on RX are nominal.

On 40m TX, I get about 1.5W out.  The signal is clean listening with my K3.  On 20m TX, I get about 2W out but there is a horrendous audio oscillation.  My P3 shows huge sidebands on the signal.

All the TX DC voltages look good EXCEPT for the base of Q7, which is supposed to be 0.7V.  I measure
 -0.895V on 40 and -0.195 on 20.  I have examined all the suggested areas, but I don't find any obvious problems.

Anybody have a suggestion of a cause of this behavior?