09-09-2020, 03:19 PM
Well, the local oscillator has abruptly quit...again. This is a very perplexing problem. I had kept it on the work bench, playing it on and off for several days, and yesterday I slipped it back in the cabinet. My confidence was high that dropping the cathode resistor on the oscillator from 12.5 K to about 8.4 K had finally kept the oscillator going. But it didn’t. It quit again. Should I consider changing the bypass silver mica? It specifies 700 pf, but I have not actually checked it. I believe I will do so.
I do not have a 36 spare tube, but I’m open to ordering one.
I’m not too eager to do a chassis rebuild for a more reliable tube and circuit, but it might be necessary.
I’m trying to understand the feedback circuit in this strange old LO. I know a grid is always out of phase with the plate, but I think the cathode is in phase with the plate. Is that correct? And so, in the schematic, there is a little coil in the cathode circuit below the primary of the first IF. Is that feeding back in phase to the plate to create oscillation? I’m lost.
Thanks.
Richard
I do not have a 36 spare tube, but I’m open to ordering one.
I’m not too eager to do a chassis rebuild for a more reliable tube and circuit, but it might be necessary.
I’m trying to understand the feedback circuit in this strange old LO. I know a grid is always out of phase with the plate, but I think the cathode is in phase with the plate. Is that correct? And so, in the schematic, there is a little coil in the cathode circuit below the primary of the first IF. Is that feeding back in phase to the plate to create oscillation? I’m lost.
Thanks.
Richard
