Hey Spec,
I have to say ... it's a bit like Christmas every day round here ....
Wake up early every morning and lo and behold another present under the tree.
Building today will report results.
Looks nice and simple, even I understand it. ( I think)
Not trying to be critical or anything .. but is there any reason you don't like this design ?
View attachment 98830
If you have problems with any tubes striking if the mains voltage is low then here is a suggested solution. The Idea is to still have the main HT supply at about 140 volts but also have an auxiliary low current supply of about 280 volts that would just be used for striking the tubes. The Idea is to feed the anode of each tube from the 140 volt rail via a diode. there would also be a feed to the anode of the tube from the 280 volt rail via a high value resistor. (Say 2.2 meg) So before the tube strikes there would be 280 volts on the anode via the resistor. This should be enough to strike any tube. When the tube strikes the voltage across it will be less than 100 volts so it will then be fed from the main 140 volt supply via the diode.
View attachment 98834
I hope this makes sense.
Les.
Brilliant guys.
I am learning a lot here.
Thanks for the waking them up suggestion with high voltage Les. I will see if I need it.
Points taken about the other circuit spec and as it stands your circuit is working very well.
I have an oversized capacitor at the moment so need to see how far down I can take that.
Mine is about 100uf @400v ... so a bit big for the job.
Although having said that .. there is still nearly a volt of ripple on it.
My experience in the shed today has been very good.
All using 240vac.... will test with just the 110 winding tomorrow and see how far down I can go reliably.
Circuit works very well and have hooked up the arduino into the op amp with a pwm input.
To get analog I just use a low pass filter with a 0.1uf ceramic and a variable resistor (at the moment for testing) to get volts out.
Seems to be the way to do it and is way fast enough for these tubes.
Final values for the transistor biasing and anode/cathode resistor are still in the experimental stage.
I am not much for calculating bias voltages etc .. so just chuck resistors in and probe around to see how efficient it is in practice.
It s a bit of a juggling act.
I can get microscopic ... movement out of the tubes with just a little code so that is great.
Getting about 0 to 3 volts out of the op amp so that is plenty of resolution for the tubes.
I found that driving the PWM at about 55 ... not the full 255 is about right for full scale.
That gets the op amp to get the 3vdc to drive the tube to the top of the bar.
These things are defiantly NOT linear though .. because at 27 PWM or so is over half scale, not by much but noticeable.
Might have to make a lookup table up in code to get it linear.
Fast .. these things are not ... tried really getting them going up and down really fast and found that I need at least a 10ms delay in code to get it looking nice.
Any faster and the top does not light up as it should. The bottom sometimes breaks away too.
Very happy to see code driving the thing up and down like a yo yo though, a real treat.
The resistor is back in as suggested and it has taken a lot of load off the transistor.
Using a 4k7 1 watt at the moment and it seems to be dropping about 50vdc across it at 12mA.
It does get quite hot and is dropping about 0.6 watts at the moment.
The transistor I was using was rated at 4 watts .. but as you have said spec that is a job for a resistor.
At the moment I am just optimising component values and trying to use a smaller transistor.
I have found after testing/abusing about a dozen of these tubes they all start off with their own personality.
Striking them at a high enough voltage seems to wake the reluctant ones up.
I have abused the hell out of the 12 I have been testing with so they probably won't last very long.
But ... any "new" tubes that fail to strike will be getting current limited to 12mA max ... and just struck and exercised to their full bar length.
Now ... I have a LOT of work to do.
Getting a some big verro board and expanding this out to 50 tubes first to see how that goes.
More to follow including final circuit.
Cheers fellas
yeah that would be better Les.If the - end of the top left capacitor was taken to the centre tap on the transformer instead of the end of the winding then only about 70 volts would be added to the main full wave rectified supply. So this would make the striking supply about 210 to 225 instead of about 280 to 300 volts. (Just a variation on spec's design.)
Les.
Morning has broken,
Off to the shed.
Question: How come we are going back to this design ? I could not get it to work the first time and it seems inefficient ?
ie: having to drop such a large voltage (232vdc) in the form of heat ?
SOA .. you say ... the mystery's of the data sheet ... is there anything that can't be ignored !?
I bought a whole bunch of the ones you recommended in the first circuit so am going to try to shoe horn them in.
https://www.farnell.com/datasheets/671645.pdf [2N6517]
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