Re: [neonixie-l] Re: Sgitheach web page update
Wow, wow, wow!! Grahame, I think if you are varying the grid current well within the design range and you see focus vary significantly enough to notice, you have a PSU problem. Either you aren't supplying the right voltage to the anode, the deflection plates are not at the right potential (in many tubes, X and Y plates should be at slightly different potentials w.r.t. cathode due to their placement along the neck of the tube), or your PSU is not regulating well (not able to supply enough current). I would measure all the voltages while you vary the grid bias and see if anything changes significantly. (Of course, even professional oscilloscopes and X-Y monitors exhibit this focus change to some degree, at extreme intensities.) (My a href=http://oscilloclock.com/protoype Prototype/a has this problem in a big way, due to the super poor job I did winding my own transformer! Aaron -- You received this message because you are subscribed to the Google Groups neonixie-l group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msg/neonixie-l/-/duFBNm0X20cJ. For more options, visit https://groups.google.com/groups/opt_out.
Re: [neonixie-l] Re: Sgitheach web page update
Hi Aaron You've confirmed what I suspected, that the focus voltage is moving enough to unfocus the image as the beam current is varying. I will take some measurements of beam current, focus current, focus and cathode voltages and try to feed the focus from a more stable voltage, perhaps using a mosfet in the control rather than the simple potential divider. The aim is automatic brightness control, probably not using the LDR in the grid circuit directly but using another DAC (or PWM) to control grid voltage and hence brightness. The LDR would be read by the AVR and acted on. Brightness control by the AVR is something I'm working towards so I can try to draw any object, no matter how big, only once rather than drawing larger objectes many times to achieve equal brightness with small objects. I have the final anode voltage set at the midpoint voltage on the deflection amplifiers. So a centred undeflected spot has D1=D1'=D2=D2'=A3 voltage. I can trim the A3 voltage for best astigmatism which I have found is slightly off the equal voltage rule, I guess because one set of deflection plates are further down the tube as you say. But I have not tried varying the voltages on the deflection plates so D1=D1' != D2=D2' for a centred spot. The deflection amplifiers are identical and fully interchangable at the moment. Of course, I've not yet progressed to CRTs with a PDA. Another change I'm planning to try is the way the octant information is sent to the blanking circuits. At the moment I hae an 8 bit bus straight from one AVR into a second that carries out the blanking decisions. This is just like yours and Davids done in discrete logic ICs. I'm going to use the SPI bus to serially send the data to the second AVR. There are a couple of advantages, it frees up a lot of pins on the main AVR that I can use for other things, but also the data sent is then not limited to 8 bits. It become easy to, for example send 16 blanking bits and so a circle can be divided up into 16ths rather than 8ths. It does look like there is time to do this easily in the object drawing cycle. The second AVR become a SPI slave and any data can be sent to it. My test trafo has been shipped from the USA and I'm hoping it'll be with me before xmas so I can build and test the new PSU. Working towards Scope Clock 2 Version 2 with ideas building for Scope Clock 3 (as above). I also want to build and case a clock for the house so I have something to show. Sent one set of PCBs to the states, another set are promised. A guy on Malta has asked me for a set, you can see is collection of CRTs and radio equipment here http://www.qrz.com/db/9H1GT But I'm waiting for the new PSU before supplying my home made PCBs. All good fun. Cheers Grahame On 12/12/2012 10:32, Oscilloclock wrote: Wow, wow, wow!! Grahame, I think if you are varying the grid current well within the design range and you see focus vary significantly enough to notice, you have a PSU problem. Either you aren't supplying the right voltage to the anode, the deflection plates are not at the right potential (in many tubes, X and Y plates should be at slightly different potentials w.r.t. cathode due to their placement along the neck of the tube), or your PSU is not regulating well (not able to supply enough current). I would measure all the voltages while you vary the grid bias and see if anything changes significantly. (Of course, even professional oscilloscopes and X-Y monitors exhibit this focus change to some degree, at extreme intensities.) (My a href=http://oscilloclock.com/protoype Prototype/a has this problem in a big way, due to the super poor job I did winding my own transformer! Aaron -- You received this message because you are subscribed to the Google Groups neonixie-l group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: [neonixie-l] Re: Sgitheach web page update
Valve [tube] filaments [heaters/cathodes in this case] generally do not have life extended by running lower power. Cathode emission is complex and heater should be run within the specs. That spec is not just to achieve maximum rated emission. Some oscilloscopes had a connection for cathode modulation of brightness. John K. - Original Message - From: Michel mic...@xiac.com To: neonixie-l neonixie-l@googlegroups.com Sent: Wednesday, December 12, 2012 7:45 AM Subject: [neonixie-l] Re: Sgitheach web page update Great design and source of information Graham! Fantastic. Just wondering about 1 thing, is it possible to adjust the brightness of the scopeclock according to the ambient light? Usually you would use the control grid of course, but what it you would adjust the current through the filament? It would both lower the power consumption and increase the life of the tube, I would expect? The IN9 / IN13 bargraph clock is my next project!! Tubes are on the way but hope I will have some time to work on it :-) Michel On Dec 12, 12:51 am, Grahame Marsh grahame.ma...@googlemail.com wrote: Hi I have added a webpage where I test a variety of other small CRTs with the scope clock 2 hardware. http://www.sgitheach.org.uk/scope2a.html This page will continue to carry updates as I trial other CRTs and other PSU configurations. I'm still extending the range of clock faces and adding multi language support. The rubidium oscillator clock workover is completed and the designs are all here. The complete software including the source code written using the free GCC -AVR C complier is available for download. http://www.sgitheach.org.uk/atomic.html The Giant 7 Jon Ellis Segment Clock page now has the software (again GCC-AVR) available for download. http://www.sgitheach.org.uk/ss.html Cheers Grahame -- You received this message because you are subscribed to the Google Groups neonixie-l group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups neonixie-l group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: [neonixie-l] Re: Sgitheach web page update
Michel Ambient light based brightess control is something I have been playing with. I remember, as a nipper, we had a valve BW TV set with a LDR in the front panel so it had a sort of automatic brightess control. But I would certainly do the control by varying the grid voltage wrt the cathode not by varying the heater/cathode temperature. My understanding, although I don't know the physics involved, is that is bad to underrun a heater. Overrunning is perhaps more obviously wrong. The main problem I have at the moment is that as the beam current is varied it pulls the focus off, adjust the brightness, adjust the focus... I've not gone far enough into finding out whether its the true CRT charactertics that are doing it or my crap PSU being pulled around :( Cheers Grahame On 11/12/2012 21:15, Michel wrote: Great design and source of information Graham! Fantastic. Just wondering about 1 thing, is it possible to adjust the brightness of the scopeclock according to the ambient light? Usually you would use the control grid of course, but what it you would adjust the current through the filament? It would both lower the power consumption and increase the life of the tube, I would expect? The IN9 / IN13 bargraph clock is my next project!! Tubes are on the way but hope I will have some time to work on it :-) Michel On Dec 12, 12:51 am, Grahame Marsh grahame.ma...@googlemail.com wrote: Hi I have added a webpage where I test a variety of other small CRTs with the scope clock 2 hardware. http://www.sgitheach.org.uk/scope2a.html This page will continue to carry updates as I trial other CRTs and other PSU configurations. I'm still extending the range of clock faces and adding multi language support. The rubidium oscillator clock workover is completed and the designs are all here. The complete software including the source code written using the free GCC -AVR C complier is available for download. http://www.sgitheach.org.uk/atomic.html The Giant 7 Jon Ellis Segment Clock page now has the software (again GCC-AVR) available for download. http://www.sgitheach.org.uk/ss.html Cheers Grahame -- You received this message because you are subscribed to the Google Groups neonixie-l group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
