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/CAPbqtvfXntXe0BABe2sFG%2Bck1u0iiFHdRm6tm-%3DBfY-fcYmXUQ%40mail.gmail.com.
