Found my error! I had retrofitted a 5V linear regulator to get Isolated+5V on my schematic. But I hadn't realised that pin 8 of the optocoupler was still connected to +5V non-isolated on the PCB! All good now. Thanks everyone.
Il giorno domenica 18 giugno 2023 alle 05:05:46 UTC+1 gregebert ha scritto: > 20 years ? Amazing. How is the phosphor holding up after 20 years ? Do you > dim the CRT (ie, with a PIR sensor or manually turning-down the brightness) > , or just let that run as well ? > > I have an 8SJ31J CRT clock kit I bought from an overseas seller (it > wouldn't surprise me if they plagiarized your design, David....), and I'm > reluctant to keep it running a lot out of concerns for the phosphor > lifetime. > > On Saturday, June 17, 2023 at 8:15:35 PM UTC-7 David Forbes wrote: > >> The Ccope Clock has a rather unusual power supply. It makes a 100kHz >> square wave for the tube heater. You can't measure it as 6.3V RMS because >> it's not a sine wave. >> When I designed and tested the transformer, I went by the color of the >> orange heater glow to get the voltage correct. It seems to work well with >> the original SC100 clocks, as their CRTs still glow after 20 years of >> continuous operation. >> >> >> On Sat, Jun 17, 2023, 12:07 AM Max DN <flata...@gmail.com> wrote: >> >>> Hello, >>> >>> Reposting with a new title for good order, as I didn't get a reply >>> before, probably because this post was comingoled in another post. >>> >>> I have built a Scope Clock based on David Forbes design. I hand wound >>> the transformer. >>> >>> All secondaries, including for the heater are on the same core, so the >>> voltage for the heather output depends on duty ratio, frequency and load on >>> the other secondaries. >>> >>> I noticed that even if I’m careful with the winding ratio, it’s >>> difficult to get an exact 6.3VAC RMS under load and the output voltage >>> would also depend on the overall load on the primary, being the regulated >>> secondary winding on the same core (SMPS regulated to +250VDC). >>> >>> So now I’m thinking to use a +6.3VDC power supply that I had designed on >>> the same board. I have rectified one of the secondary voltage to about >>> +12VDC, then I stepped it down to +6.3VDC regulated. The step-down power >>> supply works well this way. >>> >>> However when I connect the ‘IsolatedGround’ from the 6.3VDC power supply >>> to the Cathode PIN of the CRT (internally connected on this tube), the >>> power consumption increases and the focus pot gets hot very quickly, taking >>> the a full 600mA load. >>> >>> So, clearly something isn’t right in this last step, given the huge >>> voltage differential between CATHODE and IsolatedGround. >>> >>> My schematic attached. >>> >>> >> Any suggestions on how to connect the +6.3VDC isolated power supply >>> to the Cathode pin of the CRT welcome. I’m sure I’m missing something >>> obvious. >>> >>> >> Also, any tips on what RMS voltage I should read (with and without >>> load) if I power the heater straight from the secondary. This works well >>> when connected to the Cathode pin of the CRT, I can even read 6.2VRMS but a >>> test light bulb of 6.2V 500mA got quickly very dark when receiving 5.7V >>> under 450mA load, not good. >>> >>> So, not testing it on the CRT again until I get this right. I manage to >>> get a green dot on the CRT, which is a good sign. But I need to get the >>> heater voltage right before I plug the CRT in again. >>> >>> Thank you >>> >>> -- >>> 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+...@googlegroups.com. >>> To view this discussion on the web, visit >>> https://groups.google.com/d/msgid/neonixie-l/1466f997-3cfb-4861-abad-c492ef9be684n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/neonixie-l/1466f997-3cfb-4861-abad-c492ef9be684n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/d6e12afb-10e8-4cd1-85f9-1f205c916cc2n%40googlegroups.com.
