VR tube flashing?

[jarthel]

hello.

I have built a simple regulated (CCS + 0D3 tube) power supply.

It seems that there are instances where the VR tube would get brighter (like a camera flash). What does this mean? Does it mean the circuit it is powering up is trying to pull more current from the CCS than the VR tube can handle?

Thank you

[stratus46]

Originally Posted by jarthel

hello.

I have built a simple regulated (CCS + 0D3 tube) power supply.

It seems that there are instances where the VR tube would get brighter (like a camera flash). What does this mean? Does it mean the circuit it is powering up is trying to pull more current from the CCS than the VR tube can handle?

Thank you

Data sheet says at least 5mA and not more than 40mA. Are you staying within that range ? It will get brighter with higher currents but you must stay within the 5-40mA zone.

G²

[Enzo]

Think about how the glow tube works - it is very much like a zener functionally. You put a voltage across it, and if that voltage is greater than its firing voltage, it will conduct and maintain the rated voltage across itself. There also needs to be a resistor in series with the power source to limit current through the tube as mentioned by Stratus.

But you don;t draw the load current THROUGH the tube. The tube conducts excess voltage to ground (usually), leaving a steady voltage for the load. The load thus draws current through the same resistor we used to limit the tube current, NOT through the tube.

The glow tube does need a minimum current flowing through to maintain conduction. if the load draws too heavily on the supply, it can drop so much voltage across that limiting resistor that the voltage at the tube drops below the conduction level, and the tube can go out.

The harder the tube conducts, the brighter it glows, so as it nears its bottom limit, it can dim some before going out, it is not all or nothing like flipping a switch. below the minimum voltage the glow will not be reliable, but it can still try.

The key to the design here is that since the load and the glow tube share the current limiting resistor, you need to allow for both things. You need to keep current through the tube high enough for it to function but the resistor also can't drop too much voltage from load current.

The first tube in the RCA book is the 0A2. There is a nice, though brief, few paragraphs on the use of these tubes in the 0A2 pages.

And here is a chapter from the RDH with a section on designing for the gas voltage regulator tube
http://headfonz.rutgers.edu/RDH4/CHAPTR33.PDF

[Wavebourn]

Most probably you have a capacitor in parallel with the tube. Remove it: their firing voltage is higher than glowing one that depends on temperature. When fired, it discharges capacitor below glowing voltage. And so on, like an oscillator.