It's a Autodyne converter in a small AM Radio. DC voltages look ok but doesn't oscillate. Originally, the problem was a weak transistor with a hFE of 4. I replaced the tranny with a 2N2222A and it worked fine for a couple weeks and then died. Now the DC voltages look ok with about 1.5 volts on the emitter. Usually, this type of oscillator has the coil tap connected to the emitter through a cap with no bypass to ground. But this one has the tap connected through a 100 ohm resistor in series with a 3.3nF cap and then through the secondary of the antenna loopstick to the base of the tranny. This radio worked pretty well with only one IF stage, so I'm wondering if this configuration provides additional signal gain from the converter section? I plan to play around with the tranny bias to see if it might oscillate with a little more or less current. . .
+V +V | | | IF Stage winding / | \ | / 150K Feedback winding \ | | | | /c Antenna winding-----b| | \e / } \ ___ | / 100 | / \ | \ | --- / 2.2K --- 3.3NF --- \ --- | | | | | | GND GND Tap |- Primary winding-| | | |-------||---------- | | GND--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---