The PWM definitely causes the power supply to sag in my clock too. The output voltage also briefly sags, but quickly pulls itself back. As I mentioned, removing, or lessening the ripple has no appreciable effect.
> On Feb 23, 2019, at 2:59 PM, Terry Kennedy <terry-gro...@glaver.org> wrote: > >> On Saturday, February 23, 2019 at 7:22:59 AM UTC-5, Paul Andrews wrote: >> None of my other tubes exhibit this behavior (with a caveat I will get into >> in a moment). My theory on this was that the large cathodes on the CD47 >> could vibrate at lower frequencies than any other tube in my collection, >> which might explain why the default PWM frequency I was using would have no >> effect on any of my other tubes. The next largest tube I have is a CD27, and >> there is a significant difference between the size of the cathodes in these >> two tubes - 135mm for the CD47 and 55mm for the CD27. One experiment that >> this suggests is to lower the PWM frequency on the CD47 until it stops >> singing. Unfortunately, even if I lower it to the point that I can see >> visible flicker, it still sings. Another experiment would be to increase the >> PWM frequency on one of my other tubes. I did this for an IN-18, and was >> indeed able to make this tube sing too! >> >> Apart from just being interesting, this is all of some concern as I assume >> that this vibration of the cathodes, when they are dimmed or fading, will >> cause some mechanical stress, which I obviously want to avoid on a tube like >> the CD47. I am wondering if vibration could be reduced, or even eliminated, >> by smoothing out the square wave - i.e. by gradually allowing more current >> to flow as a cathode is pulled to ground and vice-versa as the cathode is >> 'released'. I would be grateful for any ideas on how to do this. I am using >> an HV5523 to control the cathodes. > > The B7971's in the MOD-SIX tended to sing as well and are also large tubes, > but not as big as the CD47. Interestingly, changing from the original power > supply to the potted supply used in the newer versions of the MOD-SIX stops > those tubes from singing as well (simple swap of the PSU board, same tubes / > CPU board / setup options). I'm not sure why changing the power supply made a > difference. My guess is that the potted supply has a large-value integral cap > in there, and that the PWM cycling was causing the original power supply to > sag in time with the PWM duty cycle. > -- > You received this message because you are subscribed to a topic in the Google > Groups "neonixie-l" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/neonixie-l/h8BMlkUhkZw/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > neonixie-l+unsubscr...@googlegroups.com. > To post to this group, send email to neonixie-l@googlegroups.com. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/04e146cc-0adc-44b7-b6b6-97a85cd401ad%40googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/83CC8B12-7BA6-4CCB-8808-9175B1A84DC1%40gmail.com. For more options, visit https://groups.google.com/d/optout.
