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 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/04e146cc-0adc-44b7-b6b6-97a85cd401ad%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
