Weirdly, the whine has disappeared. This is after I put the suspect capacitors back in. Because I had previously removed them for reforming, I wonder if one of them was not properly screwed in?
Regards Rob > -----Original Message----- > From: cctalk <cctalk-boun...@classiccmp.org> On Behalf Of Jay Jaeger via > cctalk > Sent: 07 January 2022 16:02 > To: cctalk@classiccmp.org > Subject: Re: Source for replacement caps in H744 regulators > > On 1/6/2022 7:03 PM, W2HX via cctalk wrote: > > My 2c. I am not familiar with a "whine" but certainly a "hum." Sometimes if > a power supply has seen a lot of heavy load over its lifetime, the heat > generated can begin to do things to the transformer. And once that heat has > done its "thing" to the transformer, it stays that way. And no replacing > external components will change the hum. However, there are some > transformers with bolts and nuts that hold the laminations together. > Sometimes they can be tightened to reduce the hum. I don’t know this PS > specifically and whether it falls into this category or not. > > > > I don’t know if what you are hearing is transformer hum, but if it is, you > may just have to live with it. > > > > 73 Eugene W2HX > > Subscribe to my Youtube Channel: > > https://www.youtube.com/c/w2hx-channel/videos > > This does not fall "into this category". This is typically high frequency (in > excess of 10KHz) whine, not 60 cycle, 120 cycle or even > 400 cycle "hum". > > My experience with many PDP-11 machines going back to the mid 1970s, and > those in my collection, is that this whine from the *switching* power > supplies is very common. For some people, it may be above the frequency > that they can hear. For me it is not (I could also hear burglar alarms in > excess > of 20KHz back in the day, though I doubt I could now, at age 70.) > > My *guess* is that it comes from the inductors in the switching circuit, and > is > *mechanical*, induced by the switching waveform, which in turn is > dependent upon load. If I had one that was really bad, I'd be tempted to put > on a glove for insulation and hold those to see if the mechanical pressure > made any difference. > > JRJ
