Source for replacement caps in H744 regulators

-----Original Message----- From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Jay Jaeger via cctalk Sent: 07 January 2022 16:02 To: cctalk at classiccmp.org Subject: Re: Source for replacement caps in H744 regulators On 1/6/2022 7:03 PM, W2HX via cctalk wrote: 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. may just have to live with it. 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