Moderators: Dave Moll, Andrew Davie, Steve Anderson
Klaas Robers wrote:Four capacitors of 450 V each in series is 1800 V. Then is 2100 V a little bit too high.! So add at least two extra capacitors in the right chain.....
And yes, place two extra resistors of 1M in parallel to the two capacitors connected to the AC transformer.
Klaas Robers wrote:Harry, you can't just tap the voltages that you need from the taps of the capacitor chain. As soon as they "draw current" they will drop in voltage, as the DC-current has to come from the high ohmic 1M resistors. You might use resistors of a lower value, e.g. 100k, but then at the same time you might need to make the capacitance of the electrolytic capacitors higher.
Klaas Robers wrote:But be aware that the voltage per capacitor should not go higher than the rated 450 volts. You can do clever things with resistors slightly lower than 1M to compensate for the voltage drop. I don't like it, but it is a possibility.
Good luck!
Steve Anderson wrote:You may need a low-value dropper resistor for each CRT heater - though that 7.3V will drop a bit with the CRT heaters connected, best to keep the heater voltage within 10% of the nominal 6.3V (I presume), better would be 5% which is what I try and aim for.
Don't forget your meter, especially on low-volts AC ranges, it can have several percent of error...and the calibration 'goes off' with age and often the battery voltage.
Steve A.
Steve Anderson wrote:Meter Calibration or testing isn't that easy. Where can you get an accurate source of both AC and DC current and voltage? Same goes for other equipment, e.g. Oscilloscopes. The test and calibration equipment needed is often hideously expensive and needs re-calibration itself every so often.
Some years ago I acquired a 5V regulator (from where I don't recall) that is within 0.1% of 5V. It looks for all the world like a standard 78L05 but I guess selected for the tolerance. Of course that's when new, what the drift may be over time I don't know. Add a 1k 0.1% resistor and you have a reasonably accurate 5mA DC current...though don't forget the meter will have some internal resistance.
That's all fine and well for DC low-voltage and current, but what about higher figures? Then AC? It's a specialised industry, one I admit I know little about.
[/quote]One of the easiest is time or its inverse, frequency. Even the cheapest crystal is far better than 0.1%. Get a GPS receiver and the 1 pulse-per-second output is often within 10ns (nano-seconds) of UTC time, 0.000001% That figure gets better over a longer period of time. Today you can have an atomic-standard time reference in your home for just a few dollars.
But that doesn't fix our multimeter or 'scope issues.
Steve A.
Klaas Robers wrote:Harry, you can do better, this will not work.
It depends on what you want to get.
- If you want to get +1100 volts, then you should remove the capacitors going downward to the diodes, and replace them by a wire,
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