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 <[email protected]> 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 [email protected]. >> 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 [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/67d871b5-35fb-49ef-8973-5a903a25e768n%40googlegroups.com.
