Made Colpitts and Hartley oscillators, what does the radio pickup ?

[lordvader88]

I solder'ed up a Colpitts and Hartley oscillators, about 980kHz and 720kHz. I have a transistor radio here, tuned to some random dead space, and it locks in on my circuit, and the AVC circuit sometimes thinks this is a proper signal.

Sometimes this thing squeals in the audio range, and I can influce that modulation by tocuhing the inductor

[lordvader88]

The radio is powered by the same 12V DC output wall transformer, as the oscillator circuit

I am using a Byrmen 869, which does not have very consist frequency measurements at any range it seems, I can read freq. from a few dail settings with this thing, and they often don't match, because some will read zero


for instance on AC+freq, I read 1.5257V and 0.000Hz yet if i switch to mV(AC)+Hz I get 748.0kHz(it changes a lot)

thats about what it should be by the equations

this little 1/4W inductor gets warm


So I guess its the changing conductance of the transistor, thats changing at is also modulated, and sometimes drops into AF and I hear it

[lordvader88]

well I believe A capacitor exploded, and I don't know why


wow something really blew up and i don't think it was on the radio, Colpitt's oscillator circuit, it sounded like it was the 12V 0.75A wall supply

[w2aew]

"this little 1/4W inductor gets warm"

well I believe A capacitor exploded, and I don't know why


wow something really blew up and i don't think it was on the radio, Colpitt's oscillator circuit, it sounded like it was the 12V 0.75A wall supply

Something is certainly "off" with the design if an inductor is getting warm!  Inductors would normally not dissipate power because their resistance should be quite low - sounds like you had a LOT of DC current flowing through the inductor - not something you'd usually have in an oscillator design.

[lordvader88]

No just a standard common emitter circuit, using about 25mA

So with an AM radio tuned to something random I think, its dial is taken off, it might be near the circuits frequency or not, IDK, and I don't have a working oscilloscope right now

what part of the circuits pick this up ?