02-08-2014, 12:51 AM
Jeff, howling at certain frequencies or between stations sounds like an RF or antenna problem. I assume you have the antenna connected at all points. Double check your wiring, including wire colors, against the schematic.
Check your loop antenna continuity from point to point. The schematic lists very small resistances in the coils, but I think you need only to check continuity.
There are a mica cap, a resistor, and a compensator attached to the loop antenna structure that is on the back panel. Do you have any way to test them? The resistor is easy, but the capacitors might need to be removed from the circuit to test them because their capacitance is so small that lead capacitance might mess up the measurement.
Check continuity at part 13, the RF coupling coil. It looks like a small paper cap, cylindrical, coated in yellowish wax, connected to the plate of the RF tube, 1232. It should be hard against the side of the chassis near the mixer tube socket. Mine didn't have any writing or number on it, which is the only way I knew it wasn't a paper cap.
OK, here is how I understand your problem. Correct me if I'm wrong. I'm thinking out loud, so to speak. You aligned the radio IF without the antenna connected. It went OK. You tried to align the dial with the antenna connected, but you heard strong stations across the dial while you were aligning the dial with the signal generator (a few loops of wire from the sig gen wrapped around a piece of wood or cardboard near the antenna.) After you finished aligning, you have a nasty stretch in the middle of the band, and some strong stations appear all across the band, so you hear them at multiple frequencies.
Question: does WCCO appear at its right place at 830 at all, or just at weird places and not at 830?
Have you tried to align your push buttons? It's really easy, and might give some instructive results, since each push button has its own oscillator coil and antenna tuning cap. The regular tuning cap (both sides), the oscillator coil, and associated components are cut out of the circuit when you switch to the push buttons, but the antenna and RF tube are not.
Try to align KFXN at 690 on button 1, WDGY at 740 on button 2, WCCO at 830 on button 3, KTNF at 950 on button 4, WCTS at 1030 on button 5, WLOL at 1330 on button 6, and KSTP at 1500 on button 7. If the push buttons tune to those stations with no bleed-over from WCCO or other strong stations, then your problem is in the components associated with the dial tuning (mixer tube, oscillator coil, tuning caps, etc.) If you have bleed-through from WCCO or howling while you are trying to tune your push buttons, then the problem is in the antenna, antenna wiring, or the RF tube and associated components.
I just noticed your zip code, Jeff. I lived for many years in zips 55104 and 55105, not more than three or four miles from you. I bought my first old radio, a 41-280, from a family in Forest Lake. It still has the old Twin Cities button labels on it.
PS. It is always possible that in rewiring the radio, something got connected wrong. Ain't no shame in double checking all connections.
Check your loop antenna continuity from point to point. The schematic lists very small resistances in the coils, but I think you need only to check continuity.
There are a mica cap, a resistor, and a compensator attached to the loop antenna structure that is on the back panel. Do you have any way to test them? The resistor is easy, but the capacitors might need to be removed from the circuit to test them because their capacitance is so small that lead capacitance might mess up the measurement.
Check continuity at part 13, the RF coupling coil. It looks like a small paper cap, cylindrical, coated in yellowish wax, connected to the plate of the RF tube, 1232. It should be hard against the side of the chassis near the mixer tube socket. Mine didn't have any writing or number on it, which is the only way I knew it wasn't a paper cap.
OK, here is how I understand your problem. Correct me if I'm wrong. I'm thinking out loud, so to speak. You aligned the radio IF without the antenna connected. It went OK. You tried to align the dial with the antenna connected, but you heard strong stations across the dial while you were aligning the dial with the signal generator (a few loops of wire from the sig gen wrapped around a piece of wood or cardboard near the antenna.) After you finished aligning, you have a nasty stretch in the middle of the band, and some strong stations appear all across the band, so you hear them at multiple frequencies.
Question: does WCCO appear at its right place at 830 at all, or just at weird places and not at 830?
Have you tried to align your push buttons? It's really easy, and might give some instructive results, since each push button has its own oscillator coil and antenna tuning cap. The regular tuning cap (both sides), the oscillator coil, and associated components are cut out of the circuit when you switch to the push buttons, but the antenna and RF tube are not.
Try to align KFXN at 690 on button 1, WDGY at 740 on button 2, WCCO at 830 on button 3, KTNF at 950 on button 4, WCTS at 1030 on button 5, WLOL at 1330 on button 6, and KSTP at 1500 on button 7. If the push buttons tune to those stations with no bleed-over from WCCO or other strong stations, then your problem is in the components associated with the dial tuning (mixer tube, oscillator coil, tuning caps, etc.) If you have bleed-through from WCCO or howling while you are trying to tune your push buttons, then the problem is in the antenna, antenna wiring, or the RF tube and associated components.
I just noticed your zip code, Jeff. I lived for many years in zips 55104 and 55105, not more than three or four miles from you. I bought my first old radio, a 41-280, from a family in Forest Lake. It still has the old Twin Cities button labels on it.
PS. It is always possible that in rewiring the radio, something got connected wrong. Ain't no shame in double checking all connections.
John Honeycutt
