2019-01-15 Zenith Royal 200 Conversion to Silicon

My Zenith Royal 200 conversion to silicon transistors is going slowly. Right now I’m working on getting a good sine wave out of the local oscillator (see photo). The waveform had high frequency parasitic ringing every other cycle. I put a 100 ohm resistor in series with the collector lead and it helped some. I pulled the 2N3906 out of the socket and put a ferrite bead on the collector lead and that helped a bit more. I lifted one end of the 100 ohm and put another ferrite bead on it, and it helped a bit more. At first only a single very strong station was received.  Now several more are heard. Before my modifications the sine wave had more ringing than in the photo. The photo was taken after my modifications.

I’m thinking of pulling up the end of the 100 ohm and looping the lead a few times through the ferrite bead. If that still doesn’t stop the ringing, I’m thinking about replacing the bead with an RF choke. Every time the ringing is reduced the reception gets better.  I checked to see if I had some higher inductance ferrite beads.  I found some ’73 mix’ beads and put them in place of the ’61 mix’ beads.

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