Re: SX-28A Hum
¿ªÔÆÌåÓýJim, that waveform is what I previously commented on. Looks like a base frequency of 60 with third harmonic. ?the 3rd harmonic is generated by the PT magnetizing current and it ?along with the 60 HZ coupled ?to wires in the choke circuit somehow; wiring being most likely. The location of the choke ?makes it unlikely that it is directly from the transformer. ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Wednesday, February 19, 2025 10:14 PM To: [email protected] Subject: Re: [HallicraftersRadios] SX-28A Hum ? I am not sure that the problem is resolved.? CH2 was replaced with a similar value choke with less winding resistance so it will have higher Q.? Higher Q will affect the audio filter curve so there will most likely be more ripple in the audio bandpass in the bass out switch position.? This may not be that noticeable to the ear but the scope will see it. ? In Tom's first video, at about the 45 second mark, the scope shows a strange waveform.? The main peaks are of a 60 cycle waveform.? The center peak is at 120 cycle but it's peak is negative, the two remaining peaks are at 240 hertz and positive.? There must be some nonlinearity to cause these harmonics to be generated.? This nonlinearity is acting like a diode and causing the second and forth harmonics of the 60 cycle waveform. Regards, Jim ? ? -- don??? va3drl |
don Root